Here are the completed sentences based on the context of the dialogue:
Mike: (1) What about the armchairs?
David: Sure. I'll help to put the furniture in place. (2) Can you give me a hand, David?
Mike: Where do you want the sofa, Jane?
Jane: (3) I think, the best place is in front of the window.
Mike: All right. (4) Where shall we put the clock?
Jane: They'll look nice next to the fireplace.
Mike: What about the picture?
Jane: (5) Put it on the wall opposite the sofa. Be careful! It's very old.