Hi @chilibandit , congratulations on your engagement, and on choosing a stunning dress!
I think you need to forget traditions , and do what feels right for you and your fiance.
It sounds like your GPs are wonderful people, and played a huge part in making you the wonderful woman you are today.
So have them front and centre at your wedding.
They could both walk you down the aisle!
But definitely have Grandad do it, maybe GM too.
Grandad gives a speech, also your MoH and the groom. No-one else.
If anyone else tries, groom's 6'5" BF takes the mike away and asks them to sit down.
Tell your mum now that neither she nor your dad will be giving speeches, and explain what will happen if she tries. If that's hard for you to do, ask your fiance to tell her.
Do not invite alcoholic SM.
If that means your F doesn't come, will you miss him? I don't think so. It sounds like one less potential troublemaker on the day - bonus.
Stop hinting to SiL and tell her that, just like she did, you have chosen your closest girlfriends to be your bridesmaids. If that's awkward for you to do, your fiance tells her.
Someone is given the task of bringing something for fiancé's Nan to eat.
Pizza van sounds great btw.
Do not worry about upsetting fiancé's cousins (you've only seen them twice and rarely will in the future) and especially not their children - you and fiance are having a child-free wedding, so they either arrange childcare or they don't come.
If they turn up with the kids on the day (that would be CF-ery of the highest order), the 6'5" friend politely but firmly turns them away.
In short, tell everyone who needs to know NOW what you and your fiance have chosen for YOUR wedding.
Anyone queries anything, repeat 'this is what we have chosen for OUR wedding', and don't enter into any further discussions.
Plan for the worst and hope for the best.
I hope you have the most wonderful day!