On the face of it, this looks like becoming a somewhat messy divorce with finance being the central issue and not,( as it looks by reading your post,) welfare of the children. For one thing, I don't quite understand who "they" are when you say "they say because I have not contributed to the mortgage..." Are they the parents of your husband ? Or are they the people with whom you had met for mediation ?
The best advice I can offer you from this position is that you contact a good lawyer - one who specialises in matrimonial matters. But essentially one who can display that he/she is on your side and who will push matters forward. Be assertive yourself without being aggressive. You will be aware that you may qualify for legal aid if your earnigs are such that you are unable to meet the costs of hiring a FIRST-RATE solicitor.
Moreover, accept nothing that is offered currently. regardless of "threats", which you explain as "bullying".