I imagine Jamie and Freddie were much like their uncles/namesakes (James & Sirius/Fred & George) during their Hogwarts days.
Also, Lily definitely sounded like Ginny in her first line at the epilogue "dad, when can I go." much like Ginny when Ron began Hogwarts.
Also, I think Lily will have firey, spunky, independent personality like her mum, Ginny.
I also imagine that James II and Lily II would have more Weasley features than Potter, and Al is the one left with everything Potter/nothing Weasley.
