This is an unofficial, user-friendly, guide to help you find and collect everything hidden on POTTERMORE.com
the cat, the lady sitting down, and sir c isn't working in th 2nd picture
Yes they do.The cat hisses and the harp she is holding is played. ;)
Also, make sure you actually click on Sir Cadogan in each portrait to make him talk. I wasn't doing that and it took me a while to figure out why it wasn't working.
@ Katie: Yeah, exactly like I've written in the tip. =)