As said by Umberto: Both things are possible.
You can say how many crew you have
AND
you can say if they stay on bord or bord at all.
But as said as well: At the moment only a developper can add that to the airplane. Hopefully at some time it will be possible to store those values inside the aircraft file of GSX as well, for all the planes where the dev's don't add the code, but until then, you have to live with the fact that they board.
Once again you are stretching the truth. As Umberto said in his reply earlier (No. 18):
"Yes, of course, if you know you can write a gauge, you can do it yourself, but a gauge programming tutorial is really out of the scope of this forum."
To prove my point here is a sample of xml code to set the number of crew and passengers:
<Element>
<Select>
<Value> (L:Crew)</Value
<Case Value="1">
</Case>
</Select>
</Element>
<Mouse>
<Area Height="70" Width="70" Top="0" Left="0">
<Click> 116 (>L:FSDT_GSX_NUMPASSENGERS)
2 (>L:FSDT_GSX_NUMPILOTS)
3 (>L:FSDT_GSX_NUMCREW)
1 (>L:CREW)</Click>
<Cursor Type="Hand"/>
</Area>
</Mouse>
This is only an excerpt. You will have to find out yourself how to use it.
Eisbahn