First I have to say, Bonnie and Lola are GREAT beagle names. So pretty!
we do have a chain link fence, but we check it regularly for our girls digging, and havent seen any signs of a dog going under or over.
No, no...they meant literally mate THROUGH the fence, as in through the holes...not going under or over. ;) Yep. Just checking it regularly isnt enough, you need to be outside with them watching. You wouldn't believe how quickly a random\ male dog (stray, broken loose, run out of his yard because he smelled her - which dozens within a huge radius will do once they can) can tie with a bitch in heat.
also, will they eventually (if not spayed) become on the same cycle like humans?
Do you mean two females living in close proximity getting into the same menstrual cycle eventually? Eh...possible....but wow that would be terrible, two bitches in heat at the same time running around your house! Snarkiness to the nth degree!
I also want to reiterate what others have said....a dog spends (simplified, very general version - dogs will differ but I just always though it was easier to remember it this way) "a week coming into heat, a week in obvious heat, and a week going out of heat", and can get pregnant at ANY time during those three weeks!! The bleeding time really varies, for some it is almost the full time, for others it is only middle