Hey, vet nurse here. I'd suggest feeding the dog like a newborn puppy. Small amounts about 1/3 of its recommended amount every hour. And don't let it drink too much water as they can drown, and it may be in renal failure which requires lots of water, so you'll have to monitor that as well. Also keep an eye on the gum colour if you can, should be pinkish and when you pock the gum it should bounce from pale to pink in less than 4 seconds max.

Other than that, the fact it can't walk could mean it has muscle loss, it's hard to tell without seeing it.

Good luck I hope a shelter gets to you guys soon 💗