I don't believe the Kalpoes were there if and when she died, but thought perhaps J called them up and demanded they help him get a boat, pressuring them with threats that they'd get arrested as accessories. Deepak knew the DJ, but that might be coincidence. Still rumor has it DJ has admitted someone wanted him to dump something at sea.
But Joran seems to have done as he pleased, staying out, gambling, drinking, maybe drugs, and his father didn't stop him, so Joran would have few fears about getting his father's help. This would make it plausible that he'd race home and involve his dad, whose livelihood and status on the island would plummet if this came out. Real fears for PVDS.
I don't think the Kalpoes were on the beach with Joran and Natalee either. Joran is a big greedy lustful lout, and I just cannot picture him sharing any of his conquests with the Kalpoe boys, whom Anita VDS was careful to point out...are not REALLY Joran's best friends...more on the outer fringes. She is a nasty piece of work.