My brother has completely ghosted me

So I’ve (29) never had what you would call the best relationship with my oldest half brother (48), he really never came around much while I was growing up. Within the last 10 years, things have gotten slightly better, he and his wife moved onto my parents land (my mom, our dad) and we’ve slowly been repairing our relationship. I’ve gotten especially close with my nephew (11), he was always over at my parents house and he’s a great kid.

In 2020, on Christmas Day, our dad passed away. His death was very sudden and unexpected and the grief we’ve been dealing with has been very tough. My mom had a particularly difficult time with my dads passing to the point where she moved out of their shared home and into my youngest brothers home. During all of this, my oldest brother made a promise to my mom that he would never keep his son away from her as she is his grandma.

As you can imagine, Christmas last year was very difficult on all of us. My mom had a very rough time to the point where she had to seek some professional counseling. With that said, she really was not in a celebratory mood and did not reach out to friends and family as she normally would at the holidays. Myself and my youngest brother spent the holidays tending to her as we are the only family she has. My brother took this very personally and has slowly cut off contact with her and is now not even returning my calls or messages. When I last spoke to him a month ago he told me that the lack of calls at the holidays shows him that he and his son are clearly not important to my mother so to protect his son he doesn’t think him seeing her or us is a good idea.

I asked him if he would be willing to sit and talk this out which he said he would, he said he would let me know when he was ready to talk. It’s now been a little over a month without hearing anything and he isn’t returning my calls or messages on the subject. What should I do? I was thinking of going by his house to talk to him but I’m not sure if that is the best idea and wanted an unbiased second opinion.

TL;DR: My brother has completely ghosted me and my mom, what should I do?