Caveat a house

hi
My parents had loan a sum of money to my aunty in the past and they didn't sign any document about it. My aunty only passed his house title to my parents as guarantee. My aunty and her family are staying in other places. Pls kindly advise the below questions, thank you.

1) Are we able to file a caveat on this house? As no document is sign and the loan has been more than 10 years. We only had a bank draft that my parents had transferred the money to my aunty's account.

2) How does the process of caveat work and how much will it cost?

3) Will my aunty still able to pass this property to her children if the caveat is not removed.

4) Are we able to add interest to the sum of money we had loan to her when filing caveat?