I have a little background here. My husband has two brothers: the youngest has a personality disorder of some sort and we will never speak to him again. The middle brother was a friend of ours until he became a flying monkey for his mother and younger brother.
We haven't spoken to either brother for two-ish years. The last real communication from middle brother - former friend - was him threatening us with legal action to resolve a European inheritance issue from my father-in-law's estate. My perspective is when someone threatens a lawsuit, all communication is then done via attorney. Don't pretend to make nice after going down that road.
So we just got a wedding invitation from middle brother. We're not going. I figured we could decline via the enclosed card and send a gift chosen from their registry. Any contact we've made with this family has resulted in months of abuse and threats from youngest brother, enabled by my mother-in-law. This is complicated by reports of my mother-in-law being terminally ill. Honestly, I don't know why we're invited, and I'm torn between declining immediately or declining close to the requested respond by date.