I switched my 2 yo., and weighing 7lbs, Bailey to BB 2 months ago and so far he seems to be doing fine
His food is there all day, so that he can eat when he likes. Having said that, should he appear to be gaining more weight than he should, I would feed 3x a day. His poops have been good on BB, which I check each and every time he goes. We find at dinner time, Bailey waits until we are eating, then he has his dinner too. Silly boy
Recently, Bailey has been sleeping with me and, as yet, hasn't had any accidents. Having said that, I do let him out before his bedtime at 8pm. I get up sometime between 6:30-8am and he does his business o/s then. I do keep my bedroom door closed at night, so that this eliminates his possible wandering and getting into something he shouldn't. As well, I let my 14yo cat out after Bailey goes to bed, so that she has time with us and she has the lower floor during the night. She has the upper floor while Bailey is awake since they don't really like each other, so we need to keep them apart.
BTW how cute your two are!!