Family legal agreement school fees

[Isabellahp]

Hi, I’d be really grateful for any advice on this. My father is controlling and subject to changes of minds / denials etc. He is also very wealthy and I am not as a single parent. One of my children has some difficulties and I’d like to accept an offer at an independent school which can cater for his issues. My father has verbally offered to pay ongoing. However this is causing me great anxiety as he changes his mind and denies things. I would like a written agreement set up with his offer laid out confirming he will pay until 18. (The school have set fees to 18 for me so budgeting is possible). Is there anything ‘watertight’ he could sign and if so would this be between him and the school or him and I? I would hate to disrupt my child by starting him and then having to pull him out. So thank you anyone who is able to reply with help,