How to deal with two baby raccoons? One is injured?

You need to find a wildlife rehabber in your area. Do a quick internet search and find one nearby. Most wildlife rehab centers have arrangements with vet clinics to take in wild animals, treat them till the morning, and turn them over to the rehab center when it opens. If there is an emergency vet clinic near you call them and ask for their advice. As for the one in the tree, leave it alone for now. Chances are it will come down at some point during the night. Raccoons, even babies, are natural climbers and chances are it's scared more then anything right now. If it's still there in the morning, you'll need to call animal control and they should be able to remove it. Leaving it in the tree overnight is not going to hurt it.