Water is going to be a big deal for these guys and especially with the weight of it. I've got enough of these GEN3 Stainless Steel 32 oz. Bottle & Nesting Cup Set - Self Reliance Outfitters? pathfinder 32oz stainless containers with cup & lid combo's to lend one to everyone going. ...
I've not found anything lighter than the plastic bottle the water comes in when you buy a bottle at the supermarket. I'd never consider anything like that on a hike. Be great for "car camping" but not for hiking.
Take the cup, leave the container at home.
Tell each of them to go to the supermarket and buy 2 of 1.5 Liter bottles of water. That will cover their water needs. The container weight of that 32oz stainless container is more than I'd want to carry and it holds an ounce less than a 1 liter of water but it would weigh more than a 1 liter bottle of water after you fill it. On top of all that you can burn the empty plastic bottle in a campfire so you don't have to carry it out ... but you are going to have to pack out those stainless steel containers.
If you are near a stream/pond then use a simple SAWYER filter and only take 1 Liter water bottle per man. The SAWYER filter will filter 100,000 gallons of water, weighs about 6 ounces with all the parts and is pretty much idiot proof to use. You can even screw them onto most water bottles, fill the bottle in the stream/pond and drink straight out of the bottle through the SAWYER. They are often found on sale at Wal Mart or Dicks at this time of year for about $15 (depending on the model). 1 of the SAWYERS is good for your whole group.
If you shave off a couple ounces everyplace you look you end up being a pound or two lighter overall. If you are really good you can shave 10# of weight.
I'm not an ultra-light devotee, but I will shave excess weight wherever I can find it. I don't cut my toothbrush in half or any of the hard-core stuff but I only carry the bare minimum of what I need while still covering all my needs.