Cp, if your family is using those handheld radios for comms, then they will be using the 2 meter band (144Mhz), so your quad radio would be on that band also. So your most important antenna to have would be at least a 2 meter antenna.
As far as popular frequencies, the ones people are using in your area will be the ones. There will be a few 2meter repeters in your area that will be used. Just pick 1 that works. Remember different radio bands have different frequencies. Those radios your buying will transmit on frequencies that you don't EVEN want to go there. Say like the police dept,FBI,FCC,Air controllers,and Military, and more. I highly suggest that before you even key up the Mic, that you have a total understanding of radio frequencies, which ones to stay off of, and who uses them. Above all, you need a Ham license.