I second this as I was going to say you should do
this exactly. You could include your parents though.
Far less drama and stress and closer to what you actually want without having to fight people, and upset your parents.
Arranging something your gran can eat should be easy.
There’s always the one drunk at a family party - I have no advice for you, only solidarity. But it’s down to your father to make sure she doesn’t make a scene else they leave.
For your SIL your fiancée needs to give her a hint. Who actually likes wedding speeches? Why not walk down the aisle with your fiancée?
I can understand why your parents want to be included, and why it would be hurtful to them.
It’s your day though. Do you both TRULY care about all the traditions? I PROMISE You can skip or omit whatever you don’t like.
There are multiple ways to include family in the event.
If I were getting married I would make sure it wasn’t traditional and do only the things we actually like.
No high heels for me; no walking down the aisle with everyone looking at us. Photos with fiancée before the very short ceremony. No walking down an aisle of any sort, nor mandatory slow dancing and no conga lines. Cut and serve cake straight after vows (because it never gets eaten). A magical ethereal winter wedding or spring wedding?
Children would be included & outside childcare included. I love to see children dancing and the innocence and joy they bring to festivities. Or the funny things they say and do which remind people to laugh.
Dancing? if it happened it wouldn’t be all night with all night drinking. Personally I hate dancing after a big meal. And a wedding doesn’t have to be a piss up.
No idea what I would do in the in between bar some lovely food - long tables. Maybe people would toast & say some kinds words. I would quite like a live folksy singer with a guitar actually, maybe a steel drum band performance too! Dancing would be okay here.
People can go back to their rooms and chill for a bit, so we can all have a break from peopling.
Close friends and family change into loungewear and watch a movie on a projector with comfy seating and cushions. Or another activity tbd. Popcorn, snacks, maybe some food trucks.
Morning brunch with nearest & dearest.