How can you repair a really old picture?

My grandmother gave me a picture of my great-great-great grandparents I think that’s the right amount of greats today.

I’m not sure how old the picture actually is if someone could guess for me, that’d be cool too because Grandma just said “Old”.

Anyway. Here’s the picture
I’m not too worried about the smaller cracks, just that big one that goes down the entire picture.. is there a way that can be fixed?

I plan on framing it, but I’m still worried it’s going to get worse.