Whenever he contacts you, ask yourself "what is he trying to manipulate me to get?" It sounds like you are the person with the most empathy in the family, so yes, he will target you most in attempts to manipulate/lie/deceive/coerce you. Don't get duped. Put yourself in his position and it will be very easy to see what he is trying to get out of you and why. Also, as he gets more desperate, he will change tactics, so learning to read facial body language can also help to distinguish if someone is being sincere. If he is saying he is going to change or go to therapy or something else of that nature, make him pass a drug test first, and grade his sincerity. Manipulation often uses kind tones and words, but the facial expression will be at a disconnect (ie his face will be saying he is lying when he has the right words and tone). If he shakes his head back and forth, that is indicative of lying, as well as deep blinking. There are lots of other microexpressions our faces make that we have no control over, and this can be very helpful in a face to face encounter.
One can't control his or her microexpressions on the face, and that is why that is a great tool to use when you are dealing with someone has no guilt/remorse/shame with lying.
If you watch interviews with serial killers where they ask them about their families, and if they were abused as a child, the psychopath will almost always vehemently deny it and talk about how much their family loved them and were Christian and great role models. Then you compare that to their eyes and head movement saying "I'm lying" and it becomes quite obvious. The interview with Ted Bundy a few hours before his execution is a good example of this.