Should I remove sim cards from old iPhones before turning them in ?

Oddly Apple doesn't really include that in the list of things to do for an iPhone in What to do before you sell, give away, or trade in your iPhone or iPad - Apple Support, but does for an Android (it may be because Android SIMs store more than just phone service information). It would probably be a good idea anyway, particularly if you plan on transferring your phone service to another device. If you are doing that and the new phone uses eSIM, read this article About eSIM on iPhone - Apple Support

Yes.