They'll need 3 things constantly; shelter/warmth/a dry spot to be, food and water. The milk is 2/3rds of what they need right now. Once they get past a certain point they won't have the energy or interest in eating and they will die. Sorry to be blunt but if you can't try to get something in them tonight then tomorrow could easily be too late at their age. If it's like lactaid or cashew milk I'd go for it tonight, warmed up so long as it's not too hot for your wrist (palm side). If you have both go for the lactaid, that's better than regular cows milk as it's made to be easier to digest.
FYI it's normal for them to lay on them, that's why the commercial sow pens are small, to keep the piglets alive. Just sharing so you know it's fairly common, they have poor vision so it's hard for them to keep track of them.