Florida gal here, too, though you didn't say what area you were from. Suffice it to say, however, that most hay obtainable in Florida is expensive, no matter what the type.
Depending on the age and work status of your minis, they may do better on a hay type that is entirely different than your pregnant QH mare. However, if you wanted to keep things simple, then I would choose T&A for all 3, preferably heavy on the Timothy and light on the Alfalfa. Once the mare gets into the later stages of her pregnancy, you could simply buy a bale of alfalfa and give her some extra, or feed alfalfa pellets, cubes or some other source of calcium and protein.
Personally I feed my minis about 1-2 lbs of a locally grown Tifton 44 which I prefer over our readily available coastal hay. Tifton 44 is a coastal hybrid which is generally a tad coarser than coastal (which can often be too fine-stranded for any horse( and has been developed to be more nutritious than coastal -- though that would depend on where and how it was grown, more than anything. To that 1-2 lbs of Tifton, I add a little straight alfalfa. My pasture pets get a handful; my young horses, broodmares, stallions and show horses get more (about 1/3rd of the total hay ration). I feed hay only once per day -- while they are in their stalls overnight -- because mine are all out on good pasture 6-8 hours a day (yes -- my show horses, too). Depending on where you are in Florida, your grass may tend to be "dormant" in the winter rather than freezing and dying. It will still have some nutritive value, but supplementing with hay is a good way to keep them from digging up the roots and destroying the plant itself. If you live in North Florida and your grass really does go to heck in a handbasket, putting out a good quality grass hay virtually free choice would be a good idea for all of your horses. Keeps them off the sand, away from your wood surfaces, or nibbling any questionable plants that might be hanging around your fence lines or pastures. Look for Tifton, straight timothy (get out your checkbook for that one!), or straight orchard grass (hard to find down here)as a free choice option. If the only grass hay available to you is coastal, look for a "coarser" variety that doesn't have endless strands that resemble the long runners of crabgrass.
Robin C