I have to agree with everything that Jennie has suggested.
I'm gonna go out on a limb here and do some guessing. You're home full time with three kids, all of them probably under the age of 10, and you're homeschooling which is a LOT of work. Hubby goes off to work and when he's home the pup is likely better behaved because puppy sees hubby as Alpha, but not you, and certainly not the children.
At this age, you can cut the pup back to TWO feedings per day. That eliminates one opportunity for problems. From everything I know about labs, they are chow hounds and WILL act like they are starving all the time. If your vet says to cut back the food, PLEASE do so. The guidelines on the bag are just that...guidelines. I'm guessing with 3 little kids you don't have a lot of time for seriously exercising this dog, so he's likely getting as much as a very active puppy but you're still within the guidelines. PLEASE cut back his food in line with the vets suggestions. I see more fat labs than any other breed and fat is soooo bad for them in so many health areas. And to be honest with you, if I'm hand feeding a pup that raises a lip to me (and I think that's what you meant by raising his teeth), he'd be done eating.
I frequently foster. I started with 3 german shepherds and now have 6......3 of them are failed fosters. One of the little boys has recently decided that he doesn't like having breakfast in his crate. He'll eat some of it, but then he wants to sit beside me to finish the rest. Now, normally, I'd just take his bowl up after 20 minutes and let him wait for his next meal, cuz I absolutely won't tolerate a picky eater. But, I recognize in this boy that this is his bid for more of my time and attention. He isn't being picky about WHAT he eats, but, rather where, and only in the mornings. So typically, Theo will eat the last half of his breakfast from my hand with himself and two other dogs UNDER my desk. There are NO growls, no misbehaving, and this is with three shepherds at my knees. I see it as a good opportunity for Theo to get some special time with me, and also as a good time to reinforce to the other boys that THIS is for Theo, and not get everyone elses nose stuck in my hand. With this many dogs it's absolutely crucial that they respect that something is for someone else and I can sit surrounded by 6 german shepherds handing out treats and when I say a name that's the only dog who makes a move for the treat. But, I can PROMISE you, if anyone raised a lip to me, breakfast would be OVER.
Now, as to the why....I can only guess. If this pup left his litter too soon he didn't learn dinner time manners, or even if he didn't have an excellent breeder who teaches manners, or if he came from a pet store (and most pet store pups do end up being absolute pigs because their breeding is not so good) or if he was a stray for a bit having to fight for every morsel.......when I'm fostering pups, they start off with a communal bowl, but as they get bigger and more dominant about food, I start to separate them for meal time so that everyone has a fair chance to eat without having to struggle for it. If that didn't happen with YOUR pup, he likely learned that he has to fight for his food, and he sees the kids (lower and closer to the ground) as packmates who are gonna steal his food, and you, with your higher pitched female voice as a BIGGER puppy who he just can't please, but a threat to steal his food.
Here is what I would do. To start, this pup would eat NOTHING unless he is crated. And I'd absolutely keep the children away from the room that his crate is in when he is eating. He is doing some pretty serious resource guarding and it's gotta stop. WHEN you have another adult around to keep the children totally out of the area of the house that he's in...and I don't mean they can be in the next room, but totally away from him, start to give him his food outside of the crate. Give him half his normal portion. You want to walk by him, approaching from the side and not say a word, don't even look at him.. Just walk by. After several trips by without a reaction, praise him for being a good boy a few trips by, but still don't look at him. Next, toss something super yummy at his bowl...don't worry about hitting the bowl, just casually toss a piece of meat his way. Work on this until you are able to walk right up to him and let him take the goodie out of your hand. If he growls, you've gone too quickly, so just step back a bit and repeat the earlier steps. Only after weeks and weeks of this and the behavior of not resource guarding against you, can you gradually add in the oldest child to do the same thing. This is gonna be a SLOW process so you and the kids will have to be patient. Slow and steady, and CONSISTENT is gonna win this race.
When it's time for the kids to have a snack, your pup should go into his crate with his own treat. See, to him, the bigger pups are getting all the GOOOD stuff, and it's a game. Yeah, he wants the good stuff, but he can make the other pups squeal and CHASE him when he takes their treats. So it's a game too, not all about getting the better treats, but he's clumsily trying to engage his bigger "littermates" to play. It's FUN to play catch me if you can. Eventually, you'll be able to leave him out, but only when you've installed a rock solid "leave it" and "drop it" These are probably the two most important commands (aside from come) that you can teach your pup.
The kids do need to be involved in training the pup so that he begins to see them as more than oversized litter mates. On the rare occassion that I place a pup with a family with young children I'm very clear to the parents. The kids, no matter how wonderful and well behaved, need every bit as much training as the pup. It's normal for kids (who are lower to the ground and have higher pitched voices) to get excited and to encite the pup...it's normal for them to pull on a tail or an ear until they are TAUGHT that this is a REAL doggie and it hurts them when you do that. Around the pup, the kids need to be taught not to react the way kids react...with jumping, yelling and those ear piercing shrieks. That encites the pup. So include your biggest, calmest child in a training session and let him/her give the treats. But pup ONLY gets the treat if he takes it gently from an open hand. Maybe have the child sit on a high kitchen stool so s/he is not as accesable to the pup.
Exercise is absolutely vital to this pup. Labs are very high energy and they need a chance to RUN and burn off some of that energy. Enlist the kids for this one too. If you don't have a fenced yard, install a 30-50 foot runner so pup has plenty of room to tire himself out. Let the kids throw a tennis ball for the pup, and keep on throwing that darned thing, even if he won't bring it back right away, until his tongue is hitting the ground. See if you can't find a running track or a football field that is totally fenced (be sure to take poop bags) and let him just run until he can't run anymore.
In my minds eye, I'm envisioning a young mom with plenty on her plate WITHOUT an obnoxious pup, who is alone with all 4 much of the day while dad is off working. Dad comes home, bigger physically, deeper voice and pup turns into an angel with him around and he thinks you're nuts for thinking the pup is any trouble at all. I feel for you, honestly I do!
Try to make you bigger...carry yourself with authority and try to convince yourself that YOU are the parent and that the pup WILL learn to bend to your will. Be a benevolent leader, but by golly, be the leader. And if he's rotten, there is nothing wrong with matter of factly taking him to his crate for a timeout. Not a punishment, but a timeout. If you yell and scream at him, he's gonna see it as punishment, but if you calmly take him to his crate and tell him he needs a time out, well, that's how he'll see it. Try to keep your voice lower, deeper, less female in your interactions with this rotten child too.
Alpha rolls are dangerous. Forget about those. And try to never tell him NO.....tell him what you WANT him to do instead. Catch him doing something good and praise him for that so that MOST of your interactions with him can be positive and not "that mean old mom giving me heck again". Remember that he doesn't KNOW what you want until you TEACH him what you want. Right now you need the strength of Job and the patience of a Saint, but all your hard work will be worth it in time.
And, for the record, I'm not a trainer nor a behavioralist. Just an old broad with LOTS of doggie experience under my belt, and a charter member of the "been there,done that" club.