Welcome to Gambling Therapy
Many of us will have felt the pressure you describe. 
I cannot tell you what to do but I can tell you some of the pitfalls where we do the wrong thing for the right reasons and hopefully help you make informed decisions.
The addiction to gamble is the master of manipulation and threatening to do something for a reaction is its common behaviour. Unless the person making a threat against this addiction means what they say and carries out that threat, the addiction recognises the lack of resolve as its victory.  When you threaten the addiction therefore, it will test your resolve.   If you are not strong enough to carry out your threat then the addiction has won and sees itself as invincible. We feel more powerless and the addiction takes more control. You have to ‘mean’ what you say.
Sadly we cannot ‘make’ a CG stop gambling. Only your relative can change himself and take control of his addiction. 
I take it, that it is your relative that is pressurising you to repay the load sharks. If it is then you will be paying his gambling losses and leaving him free to create further debt. You will have alleviated his problem but not helped him. 
Please write more so that we can support you further. Our helpline is brilliant if you would like to communicate one-to-one and if your relative wants to commit himself to controlling his gambling then it would be an excellent place for him to start.   To control an addiction it is important that the person who owns that addiction accepts it and takes responsibility for the wreckage his addiction has caused. 
Better late than never is excellent and it is never too late.    We will support you for as long as you need it. You are stronger than your relative’s addiction because you do not own it. Learn about it, get power over it and don’t let it abuse you – as it does him.   Your relative is lucky that you care enough to seek help on his behalf but he has to seek the help for himself which does not mean pressurising you to clear his gambling debts.
I hope this helps but please keep posting until you are ready to make ‘your’ informed decisions.
Velvet xx