Your best bet is to email them directly. Details are on their website. We received exemplary service by email and in person when there.
I never had any luck contacting them directly. You may have better luck going thru the tour agency that runs the lodge:
Borneo Nature Tours
Even then I didn't have great luck getting tour-independent reservations. I ended up using a travel agent for the first time in my life because it was so difficult to make reservation at jungle lodges as an individual.
Get an answer from Borneo Rainforest Lodge staff and past guests.