When Goku transformed straight to Super Saiyan 2 to stall Fat Boo, no one on the Kaioshin world sensed it.
That alone tells us Super Saiyan 2 isn't strong enough to be sensed from that distance.
As for Gotenks: Super Saiyan Gotenks defused into Super Saiyans, Super Saiyan 3 Gotenks defused into Base Gotenks and then the Base Kids not too long after. My personal theory is Gotenks Boo was able to push the fusion beyond its normal limits since he had it for over ten minutes. After using every last bit of the fusion, it just returns the kids to Base altogether.
There's really no consistency to Boo. We see that Piccolo Boo has Piccolo's weights on, but the Piccolo Boo from later looked different altogether. Honestly, I just look at how Piccolo reacted to the kids full-power and go from there. Trying to figure it out this way is impossible.