Hi Maggie,
My heart goes out to you! I've had to do the same with the collections of both my father AND grandfather...both excellent semi-professionals. It's very hard to decide what to do, especially as they're pix taken in both Europe and the UK. It would be so easy to just leave them on a museum doorstep like an unwanted baby, but then you'd worry about them forever.
A photo - for museum and archive collections - is only as good as its caption and date. That's a start. Chuck out anything not captioned or dated or anything that looks bad i.e. under/over-exposed or blurry.
Keep the best of what you love. Have decent sized HUGE prints made and archivally framed and keep the originals in archival boxes in a cool, dry place.
Take a holiday to Athens or Rome with samples of the very best and see if the local museums/archives are interested. You'll have a holiday, meet interesting people and make more decisions!
Or, like me, just hang on to them. We've sold some, donated some to archives but that would just be 5%. I've had some brutal chucking out days, and have parcelled some photos off to various places and instructed them to do what they wish with them.
Of course, you'll know what I do for a living - a professional photo editor! - but I could never do it for anyone else with photos close to their heart.
Good luck!
All best, Liz in Oz