They did try to keep as a group of four. The captain and first mate agreed with the tourists to swim for shore, and they were still together, after swimming a while, when they saw the plane and helicopter (which didn't see them). Swimming may have caused them to separate quicker, or it may not.

Here's some rank speculation: it sounds like the tourists were better swimmers. They say they swam faster attempting to reach the search team, and that when they failed to reach it is also when they lost sight of the crew; so perhaps the crew couldn't keep up with that burst of speed. The tourists may have thought if they got themselves rescued, they could tell the search team where the other two were. (It's possible that the crew are refusing interviews because they don't interpret being abandoned as kindly.)

I agree separating was a mistake, although I see that as a different choice to deciding to leave the boat and swim for shore. For me that partly depends on how much of the boat was still above water, which I can't figure out from reports.

When they saw the plane and helicopter, that search team was between the swimmers and land. Perhaps even though they tried to stay in the same location, they'd drifted further from land. Either that or the search team was looking in the wrong location, which seems unlikely. Either way, the four of them were swimming towards the search team, not away from it. (I think it unlikely that there was an earlier search team, closer to the boat, which the tourists didn't notice.)

(There's slightly more information in a later interview on WRKR.