Sorry to read that. You could send your mail by certified mail. They will have to sign for it. You will know it got there. If you don’t get an answer, you can tell yourself you tried. Whatever they miss out on will be on them.
In subreddit r/RedditForGrownups
In a post titled:
I've been the black sheep of my family for years and actually haven't had much contact with them for five years. How to reestablish connection with family?