The team life counters can show you how many people are in the game you are playing.
As for roller splash attack, it's only an OHKO at short range and when hitting dead on at the same time, with the exception of dynamo which you should be treating more as an enemy charger than anything. Keep them at bay with your range, punish hasty approaches with bombs, and absolutely never never never never never walk next to enemy ink that is connected to the rest of their turf, that is literally suicide if a roller who actually knows what their weapon is about is around. Additionally, don't get into cover fights with a roller - if they take cover, keep your distance and just lay down suppressing fire until your friends get there to take them out, or withdraw if you can't hold that position, even if that means superjumping. If you're suppressing someone and you hear or see a super meter complete though do something decisive immediately or get the heck out of there, because someone is about to die.
That said? One size does not fit all. Adjust your playstyle to mitigate the unique threat of your current opponents. If you play to their strengths, whether it's roller or 52 gal or chargers or blasters or whatever, you're just going to have a bad time... and that's you right now, because it's clear that your current playstyle and tactics aren't suited for dealing with splash-happy rollers.