Maddevill,
Yes, you'll need 2 units, 1 for you and 1 for your passenger, there are 2 packs on Amazon that are a bit better deal than buying individually. The picture I posted earlier shows the "hard" microphone (boom mic), the soft one is a wire with a very good adhesive tape on it and I do recommend that for full face helmets. I plan on picking up another set of the microphone/earpiece wiring so I can move the passenger unit to a 3rd helmet.
For a bit more info so you are fully aware of what you are getting:
The good:
-Great price!
-Great range (tested to a 800-1000m 2600ft-3200ft)
-Long battery (IMO, easily 8+ hours of use per charge)
-Easy to use (takes like 15 seconds and 2 button pushes to pair the 2 units and start chatting)
-Bluetooth works great, pairs to my phone and other devices effortlessly
-Universal intercom (I connected it with a Sena headset and was able to chat no issue)
-Microphone & noise cancelling works really well, I had a number of people during a phone call exclaim "you're on your motorcycle right now???"
The bad:
-Wish it was a bit louder, I can hear music and talking up to about 120km/h (75mph) but that deminishes with a headwind
-For higher speeds/louder volumes you need/want to use ear plugs... but you should be doing that anyways to protect your hearing.
-No jack for external headphones/microphone, there IS a jack there but its designed to be used with a 2-way radio.
-FM radio reception is marginal (yeah I actually use it)
-The charging cord is proprietary, not a big deal just not sure why they didn't go with mini-USB since its very similar.
This all being said, I still recommend them and I'm sure your granddaughter will love it!