Hi Nicole,
Let’s live in the present. The current reality is that you are his girlfriend. Until the ring is on your finger, you are nothing more and nothing less. As a girlfriend your job (if you choose to accept it) is to be emotionally supportive of your boyfriend. Meaning you don’t have to let his brother-in-law’s alcoholism affect you so much as to write on a forum about it.
You seem to have jumped a theoretical five to ten years in the future. A future where you are happily married to him with kids and with the boundaries you need to set.
I assure you that you would be able to say a firm, unapologetic “NO” to subjecting your future children around dysfunction.
As for your boyfriend, he might WANT to be the godfather. Lord knows the child will need at least ONE normal, stable adult in his/her life.
Best,
Inky