Can you mount a net between 2 helicopters for search and rescue?
Could you? Well - technically, yes. For a little while anyway... Would you actually do it to enact effective rescue operations? No.
There's countless issues with the idea that would make it rather impractical, but I had fun thinking of some of the challenges.
For starters, the net would end up being rather rectangular. The short edges would be as long as the arms on the helicopters could be (which couldn't get too long before they get in the way of landing, flying, etc.), but then you'd need to be able to keep good separation between the two craft so the net would be quite long and thin. The shorter the net was between the two craft, the more responsive it would be to changes in altitude, distance, etc. between the two craft, making the ride even worse. So you'd want it to be long.
You can try this at home - grab a scarf or something similar, and try and hold it out fairly flat between your outstretched arms, with a little action man or barbie doll sitting on it, while going for a walk around the house. You'll be constantly adjusting your arms to keep it flat while in motion and it's still going to be a bouncy ride for your passenger.
The longer the net is, the more drag it will experience, further exacerbating the ride as the drag would be tugging the helicopters around. It wouldn't be very long before the net is pulled tight, at which point the weakest link will fail - the net might tear, but lets pretend it's very strong - the net would be pulled off the arms, the arms might be pulled off the helicopter, or a helicopter might be pulled out of the air.
I did have an idea to help reduce drag... once you've got your passengers on the net (I'll come back to challenges with that), you could have one or both helicopters execute a series of rolls or loops (depending on whether the arms are mounted to a side, or to the front) in order to twist the net up to reduce its surface area! This would have the added benefit of snugly securing your passengers inside the twists of the net.
As for people boarding the net - you'd have to lay it carefully on a flat, open stretch of ground or water. The helicopters would need to either land or very carefully hover, coordinating the entire time in order to not tangle or crash. At which point the person boarding the net could just go for a short jog (or swim) over to one of the helicopters, and board that instead (winched up in the case of water). I'm a bit of a daredevil so I might actually still opt for the net, but in my final seconds (which began counting already when I made that decision) I'd feel pretty guilty about likely destroying two helicopters, the lives of the pilots and crew, and their families.
But oh boy it would be one heck of a ride!