So about the revival situation, the second part of the answer will be explained later in the season but the things they said are building from events in season 1. If you remember Senku and Taiju were conscious the entire time, so when the acid dripped on Senku he eventually woke up, same with Taiju.
Later they tried this method on birds and people but it didn’t work, Senku deduced that since he was thinking a bunch of energy was being used and helped deteriorate the stone, so in order to revive someone unconscious they needed a stronger acid, that’s when they created the revival fluid with alcohol and other things. With it they managed to revive birds and later Tsukasa and the rest.
What Xeno was implying is that he and his people somehow remained conscious the whole time and eventually revived, then similar to Senku they failed to revive unconscious people with only acid so he wants the formula they have.