@HappyBanshee, I'm sorry, but at this time I don't know of a way to force any births to happen, especially for the bug that exists in the strays that prevent them from having offspring. 😞
We can either wait for EA to fix this, or we can look for a 3rd party fix. I don't play with CC or Mods anymore (caused too many problems with TS3, so I'm not even trying them in TS4), so I will have to wait for EA to fix this! 🤒
The only other thing I can think of is to take your pet to the Vet an get him "fixed" and then a bit later take him back and get him unfixed. 🤔 Even if that works, it wouldn't solve the stuck pregnancy problem that you are currently having (and it might not work at all!) ☹️
I was able to get 2 CAP generated dogs to successfully mate and give birth to 3 puppies, all of whom showed up in my game. So breeding does work with CAP created pets! 🙂
In the meantime, there is a thread at the Sims 4 forum addressing this. It is constantly being added to, so I haven't read all of it. I don't think there are any workarounds at the moment. Seems we just have to wait on EA. 😢 Here is the link:
http://forums.thesims.com/en_US/discussion/928960/cats-and-dogs-issues-with-breeding/p1
I will try some expierimenting and also look around some more for a work around, but don't hold your breath! 😃😉 If I find anything I will update you. And if you find anything, please update me! 😇