What do you mean your dh wont get the every second weekend visit when the in laws return from fishing?

Why is your dh letting his ex dictate terms like that? That's ridiculous.

Your dh needs to realise he has a Duty and right to be in his child's life 50% of the time ...and well act like it. If he is not getting time with his kid then get a lawyer and take it to court. Don't just accept it when a woman says she has more rights to a kid as that's bs.
- perhaps try the mediation one last time, but have a lawyer up your sleeve.

If your dh wanted time with his kid, and that was the priority, why can't he take the ex up on her offer to stay in the spare room? Until things are resolved formally? Sure it would be awkward and it is ridiculous, but if he trusts himself there shouldn't be a problem. A father should do anything to have time with his kids even if it is pandering to the ridiculous demands of an ex..

Good luck