As far as I'm aware the easiest way to do that would be if you had houses with a limit of how many people could live there. I know that CC has a limit on the Houses.

I can hold up to 5 people per house. but then i make a new house for a new couple. now im left with a spot open in other houses where the new couple came from. their parents continue making a new baby each.
everytime i make new houses, new couples move out and older parents continue making more babys.

I want them to have no more than 3 kids. Its so tedious to hold the young couples hostages until parents too old to make babys

Can't be done. The only limitation is either by age or by the house's size.
You could wait till the parents are over 40 to open a new house, so even if there's a free spot, they're too old to have more kids, only the new couple will start having children in the new house.

is there a mod that tells when they turn 40?