Dr. Phil calls it currency! Yes, it's probably a phase. Yes, it's appropriate to let them know there will be consequence to behavior. Time outs don't work for all kids.
As long as you are calm and don't have anger in your voice you can mandate any consequence you think will have impact.
We took minutes away from bedtime. Meaning, each time the behavior was not okay, they were given a warning: If you continue, you will lose 15 minutes of bedtime.
That seems to be the precious commodity for them.
Consistency is the most important thing.
All kids go through this and for some kids it's just more extreme, no you are not imagining this!
I agree that you don't really need professional help yet.
Just be firm and consistent. Try for awhile. You can be the judge if it isn't working and you want a little help.
Wishing you the best,
Neato