Definitely something amiss there, not an age issue. It could be that moving indoors has triggered an illness, it would typically be a respiratory infection, common with temperature changes. Don't take that as to mean you are to blame, I'm not saying that, you did right in bringing them in, I've no doubt about that. It happened with a pig I adopted a few years ago, he was outdoors at the rescue, moved straight indoors here, he developed a very minor respiratory infection which thankfully cleared up with treatment in a matter of days.
As Rainbow is not eating, have you got a syringe to feed with? It would be something I'd aim to start sooner, as they need the strength from food to help them past any illness. I can email you a factsheet if you need any advice on syringe feeding, I will stay online for another ten minutes just in case you do, but will then be offline until morning.