Info: You maybe asking too much of the bride since you are treating her like a daughter and expecting all or nothing. But, wedding traditions and venue rules are really rigid.

I would split by sexes since the wedding party is, as well as immediate families. Her other bridesmaids are her sisters and then you lump in her parents, which isn't fair on your part. They are her immediate family. Your ex is an usher, which is traditionally for men only. That leaves your son and you, who are a groomsman and bridesmaid. Three of each is pretty standard.

To include your daughter, your neice would need to have 4 on each side. Is there actually room for 4 for all events? Does the groom not have a 4th person to add? Your neice might be acting petty, or she doesn't want to tell you she can't afford the bridal suite upgrade or her fiance doesn't have someone to add without insulting someone else. Without really knowing why, it seems harsh to bail on your niece's wedding because your daughter is "only" invited.