can I cite personal communication from a co-author?
You should not provide information from one co-author as e.g. personal communication since any author on the manuscript is expected to contribute to the manuscript. If there is need to state that a specific author has come up with a particular point you could do that by stating that e.g. "one of us (initials) discovered that..." or something equivalent.

In the end, just remmeber that any fact presented in a manuscript is either due to the authors or to other (referenced) sources. It is rare, but not unheard of, that a co-author may have specific contributions that require, or perhaps deserve, special mention. I would deem this quite rare. Becoming an author on a manuscript means you contribute intellectually to the end product and that includes sharing your ideas.

So to sum up, tred carefully and objectively.

By including a reviewer as co-author, you should follow regular authorship "rules". I fully realise that the question whether or not you should include the person as an author is a different question entirely so I will only focus on the situation at hand.