Rob, there are a few options to visit the valley.. and finding a land owner that would ‘host’ their visit probably isn’t the best of them at the moment. There are valid tourists concessions that are great. It’s not the same as tooling around on one’s own and all that but it is a way to visit and have no impact, and no pilikia with those that would otherwise make asses out of themselves.
I would offer to help, but I don't get to that side as much as I used to, and it really is a fragile situation between those that welcome others and those that live in the valley to hide from society and indulge their habits. So, any action not in some sort of ‘approved’ activity is just opening everyone up to a possible unpleasant experience.
As it is the best way to approach this, imo, is to consider the Waipio Valley Shuttle..
https://www.waipiovalleyshuttle.com
Their operation is run out of Waipio Valley Artworks, which is an art gallery in Kukuihaele,
https://www.waipiovalleyartworks.com
The folks that now own the gallery are new, they bought the place last year, but it is sort of a non-official gathering place for tourists in that before the road construction began a lot of the tourists concessions were run out of there, and as such I suspect they know more about the daily attitudes and what’s available and all that.
Regarding the road access and the humbug around access in general, and as background to the strife that can be felt if one strays too far from the prescribed methods of gaining access to the valley..
A handful of years ago a group of folks figured they could shut the valley to all but locals, which is all they want, by pointing out the unsafe conditions of the access road. In their shortsightedness there was the idea they could say to County that the road was unsafe and the county would give them a gate with a guard and they could live happily ever after. But it hasn’t worked out that way.
When telling County of the problem they didn’t seem to understand that ultimately if push cane to shove the county, who owns the access road, would be compelled to work towards the common good for all, not just those who had fantasies of living in a gated community, and now the road is being redesigned and constructed to provide access to the greater population and soon all their shenanigans will be for naught.
I tell this story so as to introduce the strife which everyone has been made to feel because of the selfish few who have created this drama. It is a problem, and so is all the illegal activity some hoped to hide with a gate, that is going to have to face the light of day soon. But for the moment it’s held at bay with the illusion of their privacy as the road is reconstructed. So, all said, I think it’s best your friends stick with the shuttle, or whatever other options the folks at the art gallery recommend.
Good luck!