I’ve just received a loan ($80K) and my parents are asking for $20k. My fiance is strictly against it since they haven't repaid a previous loan of $1000. On one hand i agree with my fiance but on the other hand i want to help them.
Since you borrowed $80K and you are asking about the merits of lending $20K, it sounds like $20K is likely a lot of money for you (i.e. you are not a millionaire). It is also assumed that you didn’t borrow a bunch of money from your parents earlier (they are not asking you to repay a loan) for school, house downpayment, etc.
If you do lend to family you should think of it as gifting. If you cannot afford to give them the money, don't do it. You are welcome to draft complex IOUs, but at the end of the day, how are going to get your parents to pay you back if they don’t want to/are unable to? And if you do manage to get paid back, how will this impact your relationship with your parents?
The next thing to consider is - what do they need $20K for? Is it for a large purchase or to retire debt? Is it for extravagant day to day living expenses? If your parents are in need, there are small amounts of money you can give them to survive day to day life. There are also ways you can help them to get their finances in order. This could be budgeting classes, help finding part time work, help getting access to social programs.
You will need to agree on large financial decisions such as this with your fiancé. Can you agree on a smaller amount for day to day expenses? How long will you want to continue with the financial support and when will it stop? Without jobs, its quiet possible you might need to support your parents indefinitely. Remember they did support raising you to the detriment of their finances. In some cultures it is expected for children to support their parents in old age.