It looks like a Bacterial soft rot. Nasty stuff. You need to quarantine plants immediately.
Secondly, I would reduce watering where possible, and reduce humidity.
Hopefully someone else will come in with more help.
I've found they'll be do okay at those cooler temps, as long as you keep them a tad dryer. Of course, they don't have much in the way of moisture storage, so you have to be careful.