Simon, I'm so happy that you and your son got to spend time with your brother and family at his wedding and that you had some precious time with your Dad at the end of his life.
It has always been important to my husband to stay in contact with his JW parents even though they have shunned him (necessary family business only; they never initiated contact) for nearly 50 years.
When my MIL died a few months ago, I asked my husband how he felt about her passing. He said she was, "just some crazy old bitch that hated him", so no great loss.
Now that my FIL needs help running his real estate business (he is 90 years old, and my MIL always handled the business admin), and my FIL's congregation elders have made it clear that it's not their job to care for him other than spiritually, my FIL expects a call every day at 6:30pm sharp. My husband is glad for the brief check in and has travelled 500 miles to see him 4 times in as many months, and we have just retained an attorney to try to protect him from a local scam artist.
We did not see my in-laws at all in the last 7 years. My MIL was definitely the hardcore JW, and it's hard not to feel used now. The thing is we all get to choose how we respond to other's behavior. We choose not to let others define who we are. At the same time, there is absolutely no reason to subject ourselves to abuse. Sometimes no contact, as with your mother, is the only option. It's a shame it has to be this way, but it's on her, not you.