All three are traditional musteloids (= weasels). In the LRT (subset Fig. 2) the otters do nest with Mustela, the weasel, but Mephitis, the skunk, nests between Procyon, the raccoon, and the mongoose (Herpestes).
Convergence In dorsal view (Fig. 1) the squamosal of the skunk skull has a lateral process. Where else in Tetrapoda do we find such a squamosal process or shape? 1) Coelurosauravus and 2) Triceratops.