The Olympus OM mount is not particularly compatible with Pentax, (Or current Olympus cameras, either, though not worth fussing over the kinda-sorta solution just for some Vivitars) ) but both are, IIRC, reasonably-compatible with M42 screwmount lenses (different adapters for each would be involved.)
If the lenses are made for Olympus, your father has wonderful lenses for old Olympus cameras. (Lovable, if you like film. I surely do, and those are nice.
)
If they (or some) are screwmount lenses he adapted to Olympus, then you can as easily adapt them to Pentax. Otherwise, either put em on an Olympus film body, or trade em for something that'll better fit Pentax stuff.