You said they were volunteers, so I am a bit lost. Were they British or people from a warmer country perhaps?
If they came from abroad they probably did find a British home in winter horribly cold, and the food may have been strange or even something they for health or religious reasons couldn't eat.
I grew up in Scotland, but no-one from any other country in the world has any idea of how cold Scotland can be in the winter, so no they didn't expect to be cold, they expected a house with central heating, double glazing, no draughts and an indoor temperature of 22 degrees centigrade.
They were grown ups, as far as I can see, so if they didn't want porridge for breakfast that's their problem, not yours.