Smith is definitely movable. Stephenson not so much. All in all, I hope aspiring NBA GMs learn something from this. Just because certain players have shown that they have talent does not mean they are going to fit on your team.
I see Smith returning to the Rockets as the most likely scenario though I do wonder if the Clips would want to deal him to one of their main competitors in the conference no matter how disappointing they have been so far. As far as him possibly being on the Celtics, it isn't ideal, but Smith would be a good rebounder, and if he came off the bench, they'd rely on him to give the team an offensive spark. Other teams I could see are the Kings or the Hawks. Hey, maybe the Pistons will give the Clips a call .

That's just off the top of my head because I'm sure there will be more rumors.
Stephenson is much tougher to trade because he's had this years and last years struggles that hurt his value. He still has a lot of potential because we've seen Lance be a huge force to be reckoned with in the past (That's his only upside at this point). Confession: I would love to see Stephenson play Evan Turner's role on the Celtics. This is all based on potential, but I think Stephenson as the primary facilitator off the bench combined with his tough D would greatly benefit the team. I think he's not fitting with the Clips because he's playing with guards who aren't really known for their passing with Austin Rivers and Jamal Crawford.
I would be intrigued by the potential of Smith/Stephenson coming off the Celtics bench, but I wouldn't be heartbroken if the Celtics stayed how they were.