Hello there, I hope this will help you: I moved in with my mum for a while when I was really sick (depression) and she contacted the council to let them know I was there as she wanted to make sure everything was above board. They told her that I was only expected to be declared after I was there for 6-8 months (it was a while ago, so sorry about not knowing the exact time frame) and then only if I was living there for more than four nights out of seven. So as long as he has another official residence, has his stuff there, and gets all his correspondences there, you are okay. There is no law that says you can't have your boyfriend stay over a few nights a week.

As for the fact that he is the father to your children, I can't help with that aspect. I would suggest contacting the CAB they can give you all the advice and info you could need regarding this, and they will do so in complete confidentiality.