Both me and my wife have nice (light) bikes
My 10 y.o. son has one that is not so nice (kind of heavy, not so good brakes, bought a while ago for 10$ at a yard sale)
Recently we started biking more and more (cooler weather) and:
1: it's hard for him to bike for more than a few miles
2: it's scary to go fast (brakes are really hard to apply (at least for him))
3: it's hard for me to put the bike on the bike rack and then take it off (it's heavy as fuck, like 50 lbs or so)

Can you recommend anything:
1: relatively light
2: under 2-300 used
3: available with 14"-16" frame?

Thanks in advance!