To spend time with DB

[uniqtwo]

Brief context.
I am one of 3 - youngest. Have older DB and DS.
Parents spilt up when we were young. Bitter divorce, particularly DM who tried very hard to turn us against DF.
DF has always been a steady presence in life, remarried with a child.
A few years ago there were some issues re: the new child, my older siblings and I felt they were given preference over us, but it was talked out and decided to move on.
My DS and I have a good relationship with our DF.
Latest issue;
Last year my DB decided to go non contact with our DF and our half brother. Gave no reason to anyone but we suspect it's from past issues re: divorce and DF new child.
We have not discussed it with him really as he is not open to this. He is very negative about DF
He gave DF no explanation or reason, just one day stopped all context. DM is very supportive of DB.
DF has tried to contact DB but to no avail. DF is upset and has asked us what the issues are, but we don't know. It's putting a strain on all our relationships at present.
DS has since fallen out with DB over his treatment to DF. She expects me to do the same, but I refuse. AIBU to continue a relationship with DB despite how he is treating DF and my half brother?

YANBU have clear boundaries with all of them.

Your brother obviously has some unresolved feelings towards your DF and even though your DS is trying to support your DF, it’s not her place to try and force contact between them.

I would maintain relationships with all of them, but if the topic comes up, tell them that you want to remain neutral so the only way for you to do that is to not talk about your DB when you’re with your DS & DF, and not talk about your DF & DS when you’re with your DB. Leave the room if they continue.

What whothef said!

Your brother can do what he wants. Your sister has no right getting herself involved. You do you, she does her, your DB does him. Tell your DF to stop asking you about him because you don't know, and if he carries on then it's affecting your relationship.

Have you all managed to resolve this issue? I’ve been through something similar and it’s devastating for all involved. Mine went on for years and I would say, seek help or mediation and try to resolve the estrangement.

Good luck.