OP, I hope you don't mind me jumping in here. I've never known what to say before as so many others have given great advice. I really feel for you having to tolerate this excuse for a man and his psycho mother. I'm routing for you, I really am. What's really worrying is that your posts suggest this is normal somehow and that you have to put up with it. It isn't and you really don't.
Contrary to popular belief, mums do not always know best. Sounds like your mum is in complete denial about the severity of the situation. Your dad is right this time. Find a new solicitor. You've been advised time and time again to change the locks and you really do need to get that sorted now for your own peace of mind. Ignore the people who've suggested that you check the terms of your tenancy agreement. Your safety is more important here (and will be in the eyes of the law) and the whole agreement is clearly dodgy, so I doubt they'll want to examine it with a fine-tooth comb Get those locks changed.
I really can't offer any advice that hasn't already been posted here, but the only way he is going to be able to get any of the possessions that he's claiming he has a right to is if you let him. That's it. Why are you letting him in? He is not entitled to be there or take anything from you - anything he says or does to the contrary is utter bollocks, quite frankly. You are NOT wasting police time if you alert them due to feeling threatened in your own home. Using your DD as a bargaining tool and taking your property is threatening.
FFS, stop letting this man into your home. If you must continue with your access agreement - I see no reason why you should until you've been through the courts - then let someone else do it for you at an agreed location. Ignore him. His demands and threats to take stuff will amount to nothing if you don't respond to any of it. Don't answer the door. Don't reply to his texts. Don't answer his calls. Ignore, ignore, ignore. He is a vile bastard. Stop letting him call the shots. Be ready to call the police if he tries to force entry. As others have mentioned, keep records of his texts/emails. Keep things moving with the CSA and his maintenance.
Please, please, please forget about the man you thought he was and look at what he is right now. He is controlling, manipulative, aggressive, selfish... and they're some of his finer qualities by the sounds of it. You do not deserve this. No-one does. But it does seem like you're taking some of the advice (about the tenancy, etc) while dismissing other, equally important issues - please change the locks and keep him out of your home.