After doing the mass balance calculations I'm not too happy to fly 3 up as the runway is quite short (there is enough space, but not much margin for error etc), and as I'm still relativelly low on experince I don't want to push it too much at this stage.
"If in doubt, there is no doubt."
Doesn't always work, but seems appropriate to this situation.
My question is, is it okay to take them one at a time? So go up with one, land and swap pax before going again?
You weren't, I'm sure, thinking of doing this without shutting the engine down.