rhyb - at 7 months you wouldn't really be expecting them to sit or crawl at that age. Each baby develops differently. If you're worried, get a full check up with a trusted gp. If you don't have a trusted gp, I'm happy to recommend mine. He's fantastic. As for speaking, Emily only says 'dada', and that's perfectly fine.
Are you free this week? Pop around if you like so he can have some friends to play with