What do you think will happen when James and Snow reunite with Emma and meet their grandson officially?

That is one of the things I cant wait to see! :) I have been wanting Emma to have some more scenes with Charming for a while, and it will be interesting to see how her relationship with Snow changes now that they know they are mother and daughter. Henry has known the truth since we met him, and Snow was his teacher so they spent time together but we didnt get to see much of it. , and he spent almost no time with Charming.
To actually answer your question though, I can only assume that they will work together to defeat the trouble that Mr.Gold seems to have released. I cant wait!:)

Emma will be so happy because she finally found her parents and Charming and Snow will be even more happier because they are reunited with their savior daughter and will be even more happier that they have a grandson! I can't wait to see it:)