as i have played both games, i would say it all depends.
Round 1: Samanosuke, Jubei, and Soki VS. Dante and Vergil
Dante and Vergil put up a hell of a fight but Onimusha triumphs. Jubei killed Gogandantisu, an extremely skilled swords man. If Jubei can take him, he can take Vergil. Samanosuke and Jubei are both samurai. A samurai is always calm and composed during battle leaving them with a clear mind and able to do much better in battle. Dante and Vergil are both cocky to no end, and I believe that will be their downfall. I'm not even going to mention Soki in this because I do not think he would be needed to help Sam and Jubei beat Dante and Vergil.
Round 2: Samanosuke and Jubei VS. Dante, Vergil, and Soki
Soki is the main factor in this battle. He is the reincarnation of the Oni God, hence his nickname the "Black Oni." Samanosuke later know as "Tenkai" hands over his gauntlet to Soki to use and with that power, I believe Soki can beat anyone by himself.
Dante is also a special case since he has guns. This is what i would call cheating if this was a "real life" situation. Dante would kill everyone before they had a chance to do anything. But if bullets only do damage to a health bar then as i said Round 1: Onimusha characters come out on top. Round 2: DMC Oni collabo are the winners.