When Klaus seen that Marcel had bitten Kol in 3x22, he and Elijah (I believe) gave it their all, and Marcel handled them both with relative ease. Further, he stated in 4x02 that he could kill each and every one of the Mikaelsons if he wanted to. The reason I believe this is true is because otherwise the Mikaelsons would have attacked him, instead. He has been shown to be faster and stronger, and could only be beaten by Enhanced Alaric and Lucien, both of whom we see dispatch enemies quicker and easier.
@Sean 175, Mikael would have attacked Klaus if he believed himself capable, even if he wouldn't go down easy. His hatred for Klaus outweighs his care to avoid pain. Also, Lucien's capabilities have been shown to far outweigh Marcel's, maybe not in feats but the ease with which he accomplished them. (As a sidenote, how AMAZING would it have been had Lucien knew he could compel original vampires!).
@SGP1005, I agree with everything other than the fact that the Originals could take down Lucien. Lucien bested Klaus with ease, not even having a punch landing on him. His other feats have included tackling 20 ancient vampires at once including Elijah and laughingly besting Finn and Elijah. Even Marcel took down Kol, Elijah and Klaus simultaneously.
The combined Mikaelson clan would be slaughtered.