As to the rest:
You are usually allowed to pay for a vehicle outside an IVA until the payments are finished, when they will go to the IVA.
You wouldn't have to sell your house in an IVA, but you will be expected to release part of any equity in year 4. As to the other property, I don't know what would happen about that.
You may find that unless there are special circumstances why your son needs to stay in private school that you may have to take him out.
The loan to your parents can be incuded in the IVA. I'm not sure, but if you leave it out, then I think you have to agree to make no more payments to them until the IVA has finished.
I recommend that you speak to a professional. Visit
www.iva.com for a list of companies and reviews. Give one or two a ring and you will receive free and impartial advice as to all the options open to you and the best way forward for your circumstances.