My mom has always been a bit of a pain, but in the past 6 months she's become impossible. My sisters & I think that she may have had a series of small strokes, or possibly is dealing with the onset of dementia. Her therapist wants her to be evaluated by a neurologist, but she keeps blowing off the appointments.I have a brother I grew up with, plus my mom gave up a baby for adoption in 1959 and reconnected with him 5 years ago (I call him "bonus brother"). I've developed a nice low-key relationship with BB and so he's coming to the wedding. My brother (the one I grew up with) is doing a reading and helping to usher.Now my mom's pulling some weird AW crap where she wants bonus brother to seat her at the wedding because he's "her oldest son". He's a nice guy, but I'm pretty sure he has no interest in inserting himself in our family drama (he's smart like that). And my actual brother would be really hurt if mom did this, and it would just be all the way weird. Plus actual bro and bonus bro have never met, and it would be great if that was a somewhat normal interaction.As the bride, do I have the right to tell her who is seating her? And do I just boss her around, or sic the pit bull altar guild lady on her? I really don't want her making a scene.