Do a family photoshoot on the day when your brother is over then.
Good photographers make everyone look good
We're married nearly forty years, and there is nothing we need, I imagine your parents are in much the same boat. Good wishes, having the family around and good memories, counts far more than expensive gifts I think.
The one thing I might suggest though, is that my wedding ring is wearing very thin, and I think if I ever replace it I'd go up a size from a K to an L….when my hands are sore with arthritis I can't get my ring off. If your Mum's is like that too, maybe have a word with your Dad and see if you could get her old ring remade (probably need extra gold, I have three other old family wedding rings, all well worn, that mean nothing to anyone but me, your Mum might be the same) into a pendant or locket or earrings, and your Dad could buy her a new ring….after fifty years I think she's earned it
If Dad wears a wedding ring they could both be replaced.
Not cheap, but very appropriate.
I like the photo idea, and if you could round up any of the original wedding party too for the day, and have photos of them taken as well, that would be excellent.
I hope it's a very good day indeed
M