Alan and Erin are both near-sighted, so they wear glasses.
Axel and Darren also have problems with their... well, eyes (as in one each) but it's more extreme for them since they were literally ripped out, permanently rendering them blind in that side. (At least the eye they both have left works fine so... that's good, I guess?)
Laura is both deaf and mute, and has to use sign language to 'talk' (either that or carry around a notebook at all times to write stuff down)
Carlos is partially blind and deaf, and was born with an under-developed back leg so he has a bad limp
Mizu was born completely blind and has never been able to see