What do you think Snapes friends were like about him being friends with Lily?
I don't think they would stop being his friend just because he hung out with Lily sometimes. I got the feeling that they might just sort of ignore her when she was around. It also seems like teasing Snape about her might be something that they would do as well.
It mentions in DH, that Lily's friends and other students knew about Snape and her being friends, so its not like they were trying to keep their whole relationship a secret.
There's no specific textual evidence about any of this that I can find, so this is just my opinion.
Hope it helps!
PS. I really have no idea about your first question.
EDIT: Somehow my post ended up above yours. grrr.