Just seen that this is your house - in terms of advice (not that I'm really qualified
) I would say:
Yes to furniture in the conservatory - your idea of setting it up as a dining area is a good one I think
I would put a big mirror in the sitting room - might make it look a bit wider?
I would try to make it look a little cosier - some flowers on the coffee table, and some art on the walls. I know that people generally try to declutter for the pictures, but in this case, it doesn't look very lived in and looks a little cold as a result, so I think it needs some cosy touches.