Indeed. Though we can't say for certain for now, unless we read the raws. I mean, different mangas have different rules in omegaverse ┑(￣U ￣)┍
I read the raws (here http://uploaded.net/file/t8wo02e2 , u can find more in 13dl.net ) but couldnt rly get it cuz Japanese :'D Both of the twins might be telling the truth that they're omegas (those pretty faces cant be owned by alphas FIGHT ME), but the bite marks might be done by both of them for show. But if that's the case, for what purpose? moriyo's portrayal of a/b/o is so unique in this manga that its unpredictable..
Question is are they omegas. Yes they have marks, but there has been manga where even alphas have those marks from other alphas. And one book has a beta with one but it's not a mating mark persay but made by an alpha at the request of a beta lover. I am also wondering who made those marks. Maybe they were looking for an omega and bit each other to make it look like those marks to trick the omega. I am curious. The twins are very curious beings.