Still on mortgage with ex wife but she doesn't earn enough to buy me out and i need to buy a house.

I have an 11 year old daughter who lives with ex but I can accommodate her if required. We have been divorced for six years. She pays the current mortgage. Her new partner lives with her in my old house but can't get a mortgage either. What are my rights as i am desperate to buy a house before its too late to get a decent mortgage term as I'm 47. Tried to be nice and help her out but she is doing nothing to resolve the situation. There is £60k profit and i only want £10k. Outstanding mortgage is £90k Any help much appreciated