But that is still saying, “don’t do everything you can for this guy”.
If currying political favours are standard in your area for lawyers :eek:, why should you discourage this lawyer from doing that for his client?
What were you hoping to achieve, other than trying to persuade the lawyer not to do the best job he could for his client? 
I was wondering that, too, especially since the lawyer was appointed by the court and not hired directly by the defendant.
The OP didn’t specifically say that the BIL is being prosecuted for anything to do with his wife/the OP’s sister. I’m assuming the abuse is a separate thing. He said “I told him how my brother in law is abusive” - presumably if he was being charged with abuse, the lawyer would already have known that.
If the lawyer had not told his client about the conversation and it came to light later, it might be grounds for appealing a guilty verdict. The lawyer needs to make it very clear that he was not influenced by the conversation.
Yes, all we can do is assume, given the amount of information in the OP. However, the brother-in-law threatened his and his sister’s father and the defense attorney is a personal friend of the OP. va7299 tried to use his friendship to attempt to dissuade the attorney from making a deal with the DA to get less severe punishment for his client. Even if the defense attorney ignores his friend and gives him his best defense, I don’t see how it’s not a conflict of interest, which probably is mitigated by the attorney telling his client about the conversation.
Pretty much this. It’s going to help “protect” the attorney that he disclosed the conversation, but there could still be an argument upon appeal made by the defendant that his counsel was influenced by the information, regardless of whether or not it is true.
Whether a judge would allow the appeal is another issue altogether, but the OP shot himself in the foot more than achieved his desired goals by disclosing unrelated information.
Agree with the general sentiment: he was obligated to disclose any conversation regarding the subject of the representation which could potentially have created a conflict.
The lesson here is not to talk to other people’s lawyers about their cases, even if they’re your friends.
There isn’t a prima facie conflict. Those generally only arise when a lawyer has previously represented an adverse party, and has obtained confidential information through the representation. Doesn’t smell quite right, though, and it’s certainly a relationship I would want disclosed if it was my attorney.
ETA: The attorney will certainly require the defendant to waive any conflict in writing before continuing with the case.