We've got a Three data-only SIM (12GB for 12 months) and a Three monthly plan (data, call and text) and have had no problems in the UK. The only problem we've had was when we've been outside the UK in Europe (Sweden, Norway and Italy) and tried to tether. Tethering doesn't work outside the UK on Three's 'Feel at Home' but tethering worked fine in the UK.
A few things to think about -
If you get phones through the same provider and there's no signal where you are, you'll be out of luck. If you get phones through different providers, if one doesn't have a signal, the other might. This probably won't be an issue unless you'll be somewhere remote.
We got a Three data-only SIM for my mom's iPad and it worked fine, but it messed up the contacts on her device. Her iPad is US and the SIM was UK and it put a +44 country code before each of her contacts. Most of her contacts were US numbers, so it was a bit annoying. I don't know how it happened, but it's something to be aware of if you'll be using your normal phones. It may have been a setting on her iPad or she did something without realising.... who knows.
I'd definitely suggest paying cash for your SIMs. This way, there's no worry of extra charges being tacked on to your bill or any recurring fees. That might be unnecessary, but better than seeing an unexpected charge on your credit card statement and then having to sort it out!
