A harry potter question

I was wondering why the Weasly's parents didn't know Lily and James Potter if they are in the Order of the Phoenix? Did they join after Harry met Ron? Also if they went to Hogwarts, how did they not know Lupin, Sirius, Wormtail, James and Lily?

Arthur and Molly are a lot older than Harry's parents were. Bill and Charlie were almost the same age as James and Lily (as well as lupin, sirius, and pettigrew). And, Molly and Arthur were not in the original order. They were only int he reconstituted order.

Thanks so much!