I dove with LostReef to Vandenberg as well just a couple weeks ago. The dive guide specifically told us to let her know once our air get to 1500lb. But it’s ultimately up to the divers to constantly monitor their air and let your buddy and guide know if you’re running low on air.
The four of you should split the dive guide cost. That’s what happened to us.
Technically you do need advance OW to dive that deep, but because they have dive guide, they actually let non advance OW divers go down. In generally, I think US dive shops are very flexible. When I was in Malaysia, they won’t let me dive below 18meter when I only have my OW.