Use all three. This will tell you which are best suited to the conditions in general and the difference between slopes if you need to add more.

Muhly is the largest grass of the three in bloom if it is happy there. I would plant it in larger blocks so the smaller grasses don't get lost by being too close or mixed in with it. Try as best you can to plant the Muhly where the lowest light of morning or evening will hit it. You will be amazed.

You could do the Muhly in large solid drifts. Then plant the Dropseed and Little Bluestem around those drifts in a more random pattern, some groups, some singles

Use huge amounts of solid Muhly where you can tolerate 3' height. the show will be spectacular. It's easy to grow huge amounts from seed which you can probably find from some growing locally if your city is using it.

Look to local conservation organizations for the local beach dunes grasses. Even though you aren’t right on the beach, your island is basically all beach sand, and whatever is growing locally will be happy in your sandy yard.