There's 2 Robs in my area, both refuse to play this matchup now. One of the guys is just worst than me, the other is probably better. He goes Rosa and bodies my Luigi, I have to use Falcon/Shiek to go even with him.
Rob is a zoning character, but he can't zone Luigi. His lazer is easy to shield, and if you're having trouble with Gyromite then play with items on for a bit and learn to catch that thing. It's not that hard, really. Plus fireball will stop gyro in place unless he charges it most/all the way.
Neutral
Shield lazer, catch/pick up the gyro, and camp with fire balls. Force Rob to the edge, toss the gyro in whatever direction, and use fireballs to get in. Rob has a solid d-tilt, but it doesn't combo. His F-smash can't be punished at max range, but he shouldn't be tossing that move out. D-smash is annoying, but learn how many hits it has and it's easy to punish. In brawl, rob would spot-dodge -> d-smash all the time, so watch for that.
Don't let rob force you into shield! If you're stuck in shield, rob with do the beep boop for free. Mash nair just incase, but you're probably dead.
Combos
Rob has one fast aerial, fair. It's not even fast. Just combo him mercilessly.
Rob has almost no combos, but watch for his disjoint on bair, nair, and dair.
Edge guarding
Rob is tricky to edgeguard because of how fast he can act out of up-b. However, our bair > rob fair, use rar bair and fireballs to get that damage on him while he's recovering. You can also get the dair spike, but it's risky.
Rob can beat green missile with easy, but he can't do much while you're below him. His dair and nair are both slow, you can catch him with DJ cyclone before he can do anything about it.
Stages
Ban delfino and hal bread. Take him to FD if you want to body him in the neutral, though sometimes I go battlefield to take advantage of his telegraphed recovery and trouble landing (goes both ways).
Final Notes
Rob is bad for a reason. He gets out camped, out combo-ed, and he loses in the neutral to fireball pressure. The only thing he has is the beep boop, which can kill us a bit earlier than d-throw nado kills him. If you watch rob closely, you can react to all of his aerials expect fair and upair. His ground game is alright, but we have fireballs.
Never seen a customs rob, but default is probably +2 for Luigi, which I guess is 60:40.
As for Roy, there's literally only 1 Roy and it's Sethlon. He came to a local near me recently, but I didn't get the chance to play against him. I'd say Mario vs Roy is 52:48 in Roy's favor, but that's not too useful here.