I would 2nd the bath tub idea. Watering depends on your conditions really, but if you keep them in the bath with a lowish temperature the plants will sort of slow down
when i went away for 2 weeks I left mine in the bath tub in trys. I filled the bath with water to raise the humidity and they were left like for 2 weeks without water.
4 weeks may be too long to leave plants in this 'slow' state so the other bath tub idea would be better.
The skewer trick is good, and easy way for anyone to check.
It may sound patronising to your holidays, in that case im sorry
but as you have different types make sure all the labels of the plants are visible so theres no confusion atall.