Well firstly, welcome!
..and I warn you, us ATV guys have been waiting for the next problem to pop up so you are probably going to get slammed with advice!
My first thought would be to make sure you have any fuel shutoff valves in the open position. Some ATV's have them, and some don't. It's a good idea to install if you don't have them.
Trace the line from the bottom of the gas tank to the carb, and see if there is a switch in between. There should be a plastic fuel filter, and it's not a bad idea to change them either. You should be able to easily tell the difference between the fuel petcock/valve, and the filter even without being an engine wizard.
My next bit of advice would to be make sure you have the choke in the position for starting. I'm not familliar with your specific brand machines, some of the choke levers are on the handlebars and some are on the side of the carb. If your 150cc is like the GIO's, it will have an electric choke and won't be the issue. Since they haven't run, you made need to keep fuel in it with some throttle until it warms.
Let me know if you're aware of these items and if you've tried them before I start blasting more info at you.
One last note, where are you located and how cold is it outside? A lot of discussion here of late about cold weather and good running quads, so it's possible your machines will run fantastic in the summer, and not so well now.
-TT