They’d coexisted peacefully for the duration this was at the very end. Megan is not that way with maxwell the yorkie poo but the BIL turns his purse dogs into absolutely unsocialized freaks! They told us at puppy k that there’s a window early on where you need to expose puppies to diff people and other dogs.
The optimum period is 8-12 weeks for socialization for dogs and cats but they can learn after that. It just takes longer to be absorbed. Yes, I actually had a class in Companion Animal Behavior as a college senior course. It was one of my favorite and most useful ones, in the long run.