You will also need to protect them from strong winds and falling branches from their shade hosts. I have had wind whip the leaders off of trees and had to retrain a new leader, using a side branch. A seemingly small branch from an overhead tree will strip all of the limbs from one side of a small tree or break the top off. They are very prone to this type of damage,
I haven't had any damage from excessive heat, as long as the roots receive enough moisture to supply the foliage.
Direct afternoon sun can scorch the leaves, especially if the soil becomes dry. They are shallow rooted trees and water must be provided during long dry periods. A thick layer of mulch helps conserve available soil moisture.
I would suggest that your soil be ammended with peat and compost, to retain moisture and lower the pH to slightly acidic. I grow about 30 different cultivars and the ones planted in heavy clay soil outperform those in loam or sandy soil, even with amendments. I contribute that to moisture and nutrient retention of the clay.
If they are reasonably priced, I would give them a chance to succeed in my garden, but me, I listen to no one that says "that plant won't grow here"!
Good luck!
Rb

I grow them here with success. You might need to baby them a bit for the first year, especially if it is dry, and I would also recommend digging out a 2x2x2 area and amending it before planting. Put your sandy soil in a wheelbarrow and when you fill back in, use at least half compost/peat/good potting mix mixed with what you dug out. Throw in some organic fert if you have it, like maybe some bluebonnet farms, garden tone, alfalfa meal, etc. Some amending is good to get the trees off to a good start, but don't go overboard by filling the hole with 100% potting soil or compost, attempting to push growth with miracle gro, etc, because they will eventually have to get used to your native soil and spread their roots out. They can also be grown in large containers.

I like to site them where they have some dappled shade during the hottest parts of the day. They work well as understory trees, which is what you are planning. Ever Red (has droopy/weeping branches and highly serrated leaves) does well for me, so do these two red ones I've planted that have upright branches and more of a traditional maple leaf shape - can't recall the cultivar name.

Good, deep waterings 2x a week (in the absence of rain), especially the first year help to get them established. Also, mulch well. Shredded leaves are great, because they will continue to feed the soil and will also help to keep temp and moisture levels more even.