Thanks everyone. This forum and all your advice has been a godsend. This is also ridiculously stressful, think I may move to rehoming exbats after this!
They're cuddled up, no cheeping. In a row not a ball though. They aren't touching it at all lying down, gap of 2cm/3cm maybe. I might try and stick a bit more wood shavings under there after all, but to be honest I guess they need to rest right now. None have come out yet, so they don't know about food/water - shall I wait until tomorrow to fish them out and dip their beaks? If they don't come out by then I'm assuming they're a bit cold still too?
There's a thermometer in the woodshavings, under the Ecoglow but not touching it. Currently 29degC but still rising.