I'm part way through my father's slides, and I have a long way to go!
My advice would be to spend a lot of time first organizing and then viewing them with a hand magnifier, with a view toward making hard edit/discard choices at that stage.
I use one of these to do that - thrift stores can be your friend:
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I swapped in an LED replacement for the bulb to keep it cool.
As I go, I try to put them in date order, and make notes about subjects in a written document that is easily edited.
If your family is like my Dad, there will be lots of flower pictures and the like that can be added to the discard bag.
With that process done, you can revisit whether you want to invest in equipment, or pay someone to do it for you.
If you organize and catalogue them first, you can consider getting relatively low resolution scans done commercially, and then using those for sharing and investigating whether particular slides warrant higher resolution results.
If you develop some sort of cataloguing system, you may wish to consider adding handwritten codes to slide mounts.