If speaking to a family member (who you haven't seen for a long time, say over the phone and you don't know who you're talking to), will dochirasama desu ka sound too polite, or is it okay to just say dare desu ka?
Dochirasama desu ka (どちら様ですか)
Is too formal for a family setting. It would be used in extreme formal setting, such as buisness or talking to strangers.
Dare desu ka (誰ですか)
Works completely fine, but it you would like to be just a tad more formal Donata desu ka would be best.
I hope this helps! Please notify me if anything is unclear.