Yes members are allowed to sign in one guest. The information is at the bottom of the page in red on these two pages. Note that the fees for the Glen Brittle hut are now £3 per person per night. I don't know the current fees for teh Macintyre hut.
In reply to Barry Chocolate: Used to be able to get the key from hotel next door(Rhs as you face hut) Excellent doss btw!
Best not leave any valuables as its sometimes open inadvertantly when groups are in and out during the day.