So would the only equity available if you sold the house be the �50k plus his dad gave you and which would more than likely be given back if you did sell thereby leaving you both with nothing to get somewhere new.
Would your partner financially support your youngest child and the other children, depending on their ages.
If you are still on the mortgage and, in any event, in the property then it could be said that you would more than likely have the right to stay there with the children until they are a certain age so would you get state support?
Some info here on housing benefit and who is eligible...
http://www.dwp.gov.uk/lifeevent/benefits/housi ng_benefit.asp
I'm guessing you can't pay the morgage now as you're on maternity but did you pay the mortgage before and could either of you pay for a mortgage on the property alone for the forseeable future?