Should we chair a session in which we present?
If the conference has asked you, there is no reason not to. Of course, chairing can mean different things depending on the conference. It may be just introducing speakers or keeping them to a schedule, or it may be actually chairing a discussion. There are other possibilities, I suppose. 

I don't foresee any conflicts in such a situation, though you may want to accept or defer any responsibility for it depending on your comfort level.