Oh my! There are already many threads on this. You can search them.
If I were you, I would finish family then do psych as post-master (if you still want to). Since you already started, I would not throw money and time away and switch. The expanded medical knowledge will be helpful for you in some psych NP position. As u see on this board, there are also psych NPs who went back for FNP for expanding medical knowledge.
FNP is a board specialty initially but gives you the long-term opportunity to specialize in a much more lucrative fields (ER, derm, hospitalist NP, pain management).