only for families. I don't think FM
would work because we are riding in a lot valleys and hills.

I don't think handheld CB is going to do any better around hills. You need a
quarter-wave antenna with a good ground plane (such as a car would provide)
to get any real range with CB, and even then hills will still block a lot of
the signal.

You actually could use GMRS but each person would need their own $80
licesnse. They call FRS the Family Radio Service because the FCC didn't want
a bunch of yahoos cussing and jamming as may happen from time to time on CB,
but non-family members are certainly still allowed to communicate using FRS.

I recommend you stick with FRS an deal with the line-of-sight issue. If you
are biking in a long line, people in the middle can pass messages to those
in front and back as you crest or round hills.

If you need more range, you could go to MURS. Four times the power, and at a
frequency that will bend around hills a little bit better. You can also use
replacement antennas ( = better range). However, MURS radios cost $100 and
up vs. FRS which cost $10 and up.

There are some Chatterbox FRS units designed for motorcycle helmets, these
may work on a bicycle helmet.