I'm trying to set up a multicam clip with footage from 2 EX1s (XDCAM Codec 1080i) and a Z7U(HDV 1080i). I keep getting a message the the frame sizes don't match. I am not sure what is the best way to handle this.
Do I need to convert everything to Pro Res? Could I just convert the HDV footage to something with the same frame size as the EX-1? My HDD is starting to fill and I would like to do as little converting as possible. My sequences are set up for XDCam and to render effects in Pro Res. Any suggestion would be appreciated.

Set up a sequence in ProRes in the frame size that matches your XDCam footage. The HDV footage will drop in and play although it will require a render later. You should be able to set up all three sets of footage as a multi-cam clip and switch. I've done it with mixing different varieties of HDV but not XDCam. Try it.