Ok, please remember that I am an old Soldier, so, my advice tends to lean towards the "big stick" approach. Just saying. Take it for what it's worth.
There are times that Christians, because of their compassion, love, and concern for others, act in ways such as you. Allowing people to SURELY TAKE ADVANTAGE of them. IMO, God does not want us to do this. Reason being, is that when we allow others to treat us in such a way, we become "enablers." Meaning, our acceptance of their treatment of us allows them to continue acting irresponsibly, and immaturely.
We would not raise our children in such a way would we? Neither should we raise our friends in such a way. Personal responsibility is a NECESSARY lesson that must be learned. Now, IF your family member DID NOT have the financial resources to MEET their obligations, THEN it would be Christ-like to COVER them. HOWEVER, IF they are doing as you state, THEN in my opinion, this is a sinful way to treat you. YOU ARE NOT A DOORMAT. You are a Child of God!
[ok, Old Soldier part]
Snatch 'em up by their scruffy neck, give 'em a good shaking, and then set them down and let them KNOW that you are not their personal ATM............THEIR FINANCIAL RESPONSIBILITIES are THEIR FINANCIAL RESPONSIBILITIES. Financial responsibilities COME FIRST. Now, if they have money left over...........well, it they want to blow it eating out every night and partying........that's their irresponsible act.........BUT PAY THE BILLS FIRST.
If they can't do this, hey, U-Haul is just up the street.
God bless