Historical unpaid maintenance

Hi all, wondered if anyone could help and/or advise please?

So my father failed to stick to the court agreement to pay my mother weekly maintenance for my sister and I. He actually stopped in 1990 so working this out including interest accrued is a pretty heart sum. He has children from a previous marriage and also step children. I know he owns a property which has increased in value substantially, this property has a caution registered against it by my mothers solicitor many years ago. The land registry deeds show he is the owner, also give a U.K. Address for him and I have found him living abroad via internet research and information from his first wife.

My question is how can this be progressed to request the release of funds for my mother to be paid what she is quite rightly owed. She has worked incredibly hard as a single parent and I feel deserves to be given what is owed to her.

Many thanks in advance for your help.