Ok Bulborbish, I looked through the movesets... finally. Sorry it took me so long. Some thoughts (that kind of turned into big walls of text
):
Overall I like the Sireno/Sirena lines. I feel like Sireno could use another move or two, though (it only learns 5 moves before it evolves at 27... that's kind of not very many), maybe Karate Chop or something like that between 16 and 23? I know it's only water at that point, but regardless of how useful it is it's some flavor and something to keep the mon interesting. Also, someone mentioning breeding made me realize you'll want to bump down their first moves to level 1. I THINK newly hatched mons are level 1 in Gen 3, so if we end up getting breeding in, newly hatched Sirenos/Sirenas won't know any moves the way they are. Maybe even add a new move at level one for each of them (Comet Punch for Sireno, Double Slap for Sirena?) to fill them out a little more.
Scamps feels ok, but not particularly legendary, especially when you compare its moveset to Dorfmentus, which is better in almost every way. I know that moves don't necessarily make a legendary great, but.... yeah. I'd say add in some things that make it hard to hit (maybe Minimize/Double Team and Sand Attack/Mud Slap?), since that's a theme that might go well with a cute little cat legendary and they can make whatever mon they're on really frustratingly overpowered in a lot of circumstances. The problem with that suggestion is that, while that might make a powerful mon, it still doesn't feel legendary for some reason, so other suggestions would be great.
Dorfmentus... wow. Is that a pseudolegendary/legendary? That's a seriously powerhouse moveset, especially if Dorfmentus is Psychic/Fighting (which I'm not sure about). It could be ok as-is if it's supposed to be really good, but if not, you might want to get rid of a theme or two. Some ideas are: take out Dream Eater/Recover to make it less durable, take out Bulk Up/Calm Mind so it can't snowball as much, take out Confuse Ray/Kinesis so it can't control as well, or take out some of the high end powerful moves. If it's a normal Bayomon then I'd say probably any two of those would be necessary, maybe adding in basic one stat boosting moves to fill the gaps.
The Boogesh line looks great though!
I do like the dynamic of it learning a pretty good move at level 1 but it being mostly useless until it learns Hypnosis later unless you get to a move tutor/relearner and have it relearn it there.
Edit: also, these are all just my opinions, definitely not gospel. Feel free to say "umm nope, I was going for something, I'm going to keep them how they are" if you want. I can already tell we aim for different numbers of moves (you seem to go for 11-13, I go for 18-20) so I know we do some things differently. Just wanted to give what input I could.