Do I lend/give money to a close family member?

My brother-in-law has been out of work for 5 months and asked me for nearly $10K today. The money will help pay medical, auto and basic needs for his family of 5. He is “80%” sure that he will be employed within 30 days with a very reputable accounting firm but, historically speaking, he hasn’t been able to secure or retain such a position since his bout with addiction 7 years ago (and has remained sober ever since.)
I am torn because I “lent” the family $20K 6 years ago and they remain underwater to this day. He is a former executive but has a history of some poor decision making despite his brilliance.
I am a single mom who, in another lifetime, earned some $ but am pretty worried about my own future now that I am earning much less and am feeling as though a “loan” will further enable the situation. However, I feel terrible with this kind of tough love approach and love my family deeply. This won’t be a loan if history repeats itself.
PS: My sister is unaware of this request…their marriage is struggling at this point due to this never ending situation.
Any advice?
Where is that fine line between helping and enabling??
Thank you.