Actually, Uller, before the gnomes say anything--...
Yes...just to review, I don't see the 0 hp/Stable state as being knocked out but more akin to someone who is just so badly injured they simply can't perform strenuous actions, move, stand, cast spells, etc. Imagine any movie or book where a character is down but able to talk a bit ("Stay golden, Pony Boy"). So yes, you can talk to them. Having long, in-depth conversations might not work out but some talking is possible.
Ezraen's pre-fight 25 persuasion check convinced Topsy that you are friends. However, after experiencing what she has experienced, her only desire is to die. She has no faith in finding a cure any time soon. "It is like rats are devouring my soul." The thought of her brother going through it is too much for her and she begs and cries for you to kill them both. Turvy for his part just lays there, not moving, not making any noise and staring into nothingness.
You don't know what causes them to transform. All you know is they've been struggling with it for sometime. On the surface it is the moon. But in the underdark? You just don't know. You do know that they didn't transform back to gnomes until they were reduced to 0 hp.
Bertram is definitely not for healing them and is for tying them up. His reasoning: They're dangerous. They concealed their curse and put you all at risk. They can't be trusted. He'd rather cut them loose than take them back but then what if the drow get them? So he's willing to put up with taking them with you if you don't want to take the mercy kill route.
So...discuss your plans. Tell me what you want to do before you head back to the group.