I'm going to skip Raiu until Notdeadyet addresses LeeRoy's initial concerns, so next up is Jin.
First: The man himself is fine. No problems there. Though the time it would take for a target to develop the symptoms of radiation sickness would be of no use during a fight. Just keep that in mind.
Second: What is the targeting method for the high power precision shot? Is there a laser that Jin has to paint the target with? I would also recommend switching to a particle rifle instead of an actual bullet, that was the power level of the shot could remain within tier 3. If Lalliman's math (and my own) is correct, the bullet would be traveling at mach 234.6, which would blow through any defenses anyone in the arena possesses. By switching to a particle rifle, you can maintain the 2 second travel time while also reducing the power of the shot to acceptable levels.
Third: The mech is going to need a lot more detail, and as it stands now would be a tier 5 summon. In addition to what Lalliman said about speed and the power of the photon lasers (which are already iffy due to being as fast as light and requiring no charge time), we'll also need to know how much ammo it carries for the autocannons, how durable it is, and if it increases his strength at all (and if so, by how much). Anything you can add about its sensor and targeting systems would also be good. Regarding the photon beam cannon, as long as you don't consider the "and armor" portion of the damage description to be gospel, it should be fine. If the "and armor" part is taken literally, it would give him the ability to utterly destroy even tier 7 armor in one hit, which is not okay. Since LeeRoy already has a character with particle weapons that travel at near the speed of light (and require charging time), I don't see an issue with this one as long as the charging is visible.
Fourth: If "extremely durable" means what I think it does, that trait alone puts both droids at tier 3. That, combined with the near-perfect accuracy and armor piercing assault rifles of the XC1 and 2, would likely bump them up to tier 4. If they only had average human accuracy, rather than the accuracy of an infallible machine, they'd still be tier 3. The axe wielded by the XR1 is definitely at least a tier 4 weapon though. Titanium melts at around 3,000 degrees fahrenheit, but in order to cut it like butter the axe would have to be considerably hotter than that (and this is without taking into account the fact that you mention alloy, which changes the equation depending on what it's alloyed with). His reaction speed should also be more clearly defined, since there are a lot of things that are faster than a human can blink. I really like his backstory though. It gives him a really cool dynamic right off the bat.