When I left my ex of 9 years my brother and sister in law (especially her) wanted to keep inviting him to events. We remained on good terms but there was no need for us to attend events together.

I told my brother and sister in law not to do it under any circumstances. their loyalty with me, not ex. So they refrain from that.

Plus I intended to start dating fairly soon and had no desire to make my ex feel awkward or upset him as I was the one who left.

Now if you two end up in a big group or want to stay in touch, that’s fine but why is your brother actually inviting him? I don’t think it’s appropriare for family members to invite exes without consulting. It’s not a very proper thing to do. Your brother is putting you in awkward position.