TL;DR : MOB wants to invite groom's estranged-ish step-grandmother, against the wishes of the groom and his family.
Ok, details. FOG's parents divorce long ago in a galaxy far far away. Grandma got remarried to step-granddad, who later adopted FOG. FOG lived with grandma and step-granddad throughout his childhood. Grandpa got remarried to step-grandmom. Grandpa and step-grandmom live in the same town as MOB. MOB meets grandpa and step-grandmom after B&G start dating. MOB and step-grandmom get along well (same ethnic background, go to the same church). For whatever reason, MOG and FOG are not close with grandpa and step-grandmom. Grandpa gets sick and passes away (Groom and family visit hospice and attend funeral). Grandma get sick and passes away. Only remaining grandparents are step-granddad and step-grandma.
Bride asks both parents for guests lists. MOB, as she is paying for the reception, sees the complete guest list and notices step-granddad is on there but step-grandma is not. Questions the bride about it (repeatedly) and is told to drop it. Bride now finds out she is pressuring to groom to include step-grandma in the guest-list. Groom talks to POG, who both say they would be "uncomfortable" with step-grandma attending. MOB not told this yet, but imagine a shit-storm on the horizon.
(Switching to "I" now, because writing "bride" all the time sucks) I'm really pissed she's putting pressure on FI about this. I have nothing against step-grandma, but I'm in the camp of "Not my family, not my decision." My mom really thinks that it's "right" that step-grandma be invited, and she keeps saying that step-g doesn't have to be seated by FI's parents, but unless she sits with my mom, she's not going to know anyone there, and FI said his parents will avoid step-g all night. Mother also says step-g is one of "her friends" but as the guest list stands, my mother is already inviting more of her friends than me and FI combined (irks me, but not my hill to die on). We are also very tight on the guest list right now, and 1 person might not break it, but I want to refuse on a manner of principle.
My stand is that I should be behind my fiance on this one; according to him, there is "no bridge left to burn" in this relationship and while he seems a bit ambivalent about step-g's attendance, if it makes his parents uncomfortable, he supports them. Am I doing the right thing by supporting FI on this? Should step-gma be invited no matter what? If my mom's paying, does she get to overrule someone else's comfort? I feel like I'm doing the right thing, but you ladies always seem to know what's best, and I really appreciate your opinion.