It's always an issue, as there is always the deeper dive first, more often at Palancar. We have well over 30 years each and thousands of dives, live on the island, but prefer to just tool around in the shallows rather than hang on a fishless wall at 80'. Even with a boat of beginners, there is a still the norm of deeper dive first. You can vote for shallower sites, but you might not win. You can also vote for shallower "deep" sites, like Cedral Wall, San Francisco, or LaFrancesa, Palancar Gardens but it might not go over. If you hire a private dive guide, you still may be on a deeper site, but you will have a buddy with you if you dive it shallow. We dive the top edge of the walls where there is a lot more fish action when we go to the deeper sites. It's pretty easy. You are still within easy visual distance of the group. You may also find by the second day that 70' isn't much different than 40'.
Back in the day, our favorite dive day, was Cedral followed by Cedral, LOL Tomorrow we will dive Yucab and Paradise grass, saving tons of fuel for the boat while hunting for small critters. Good luck and don't fret. It will all work out.