As far as I've experienced it does not combine families unless there is a marriage involved.
When it comes to pregnancies I have that turned down to 0 % as I want NS in game to handle that. I have also turned off homeless move in and homeless marriage, as I want to control who lives where and who is generated. I regularly remove all homeless sims as I have enough sims in my game. I have also turned down marriages by a lot, because I felt it was over enthusiastic about marriages. I like it around 5%, and checking once a week, that usually means 1-3 marriages a week. When I feel there are too many singles, I up it to 10% for a few weeks, then go back do 5%.
I never have MCCC change names for my sims, I do it manually after a marriage, as I like to keep track. I use double names when possible or create new ones of their names so Janvier + Rivers ended up being Rivier and Andersson and Stokton ended up being Anderton.