Mum Wants Money From Sale

Hey guys, greetings from Australia.

I'm here to seek some opinions.

I have recently sold my house of which my parents helped me buy by being guarantor and using there house as security for the loan.

When my wife and I bought this home my parents insisted of being on the loan with us because they were going to stay with us as dad has parkinsons and health care is more accessible here in brisbane rather than Gladstone where their house is.

When going into the agreement we discussed that they won't need to pay us any rent or chip in for any bills as we were just happy that they had helped us buy our first home.

In order for their half of the loan we paid money into their bank account for the loan money to be deducted. This was even requested by the bank manager who issued the loan because she knew that with them on a pension she knew they wouldn't be able to pay. Which of course we're ok with because it is our house.

Fast forward 5years my mother insists now it's her house and she is entitled to half. This had only come about because Brisbane house prices boomed during and post covid.

Never ever before this and with the agreement of they live rent free and just cook for us now and then was this ever mentioned. And now she is saying no one told you to pay mortgage on your own, she says "I could have paid my half". But if that we're case why have their bank account details and the bank manager ask if that's OK.

Now that we have sold the home she is demanding 100k from the proceeds of the sale. Which part of me is ok with that but the other part being my wife isn't. Because not one cent of theirs went towards paying any part of the house mortgage. And that is all mine and my wifes hard earned money.

If this were to get messy and go to court what do you guys think the outcome be. Or just general thoughts on the situation I'm in is appreciated.