Last year in track my daughter crushed her times in the mile/2 mile on lower mileage (20-30mpw)/higher intensity (state champion in both events/2nd in 800). She increased her mileage in the summer (we live in the south) and into XC up to 40-50mpw. By the middle of XC, she was slower than the previous XC season and was struggling with workouts/races where her legs would burn early on in the runs. Took her in for blood work, and she had become iron deficient.
For winter base, she tried to maintain her mileage while taking iron supplements, eating more red meat, etc. Her iron levels improved but then she developed a stress reaction in her femur that has cost her her track season. Increased risk of injury is common in iron deficient runners.
Girls are much trickier to coach than boys, and it would be advisable to keep close tabs on how each girl responds to training. Some can handle the mileage without injury/iron deficiency, some (most) can't. For those that can't, it might be a good idea to limit running mileage to maybe 4-5 days/week and supplement the rest of the time with cross training, such as the bike and aqua running. Or, if doubling, cross train 1.5-2x the running time on the bike/in the pool. Another idea is to give the girls a day off after long runs to decrease chance of injuries or limit long runs altogether. I have come to believe that too long long runs are what increase the chance of injury the most, especially when moderate to hard progressive running is tacked on the end of the run when legs are tired. Also, for workouts, do the harder intervals early on fresher legs.
I think it's a good idea to vary the daily mileage, so the girls aren't running the same number of miles each day. The rest/recovery days are vital. Also, getting the girls stronger through 2-3x week of core/strength training is important. Limited hill running/sprints can work for strength, but be careful with this, as early on, it can cause injuries if too much done, too soon. Also, too many runs in the hills and downhill running can present injury issues.
I am going to predict that the majority of your girls will become iron deficient with the training you posted without iron supplementation, eating more red meat, etc., especially if they are still having their monthly periods. You live in the south, so the girls are going to be sweating a lot, regardless of when you run. The a.m. runs will be cooler, but more humid.
Although my post is mostly anectodal, I have done some research and found this is a very common occurrence when young girls/women attempt to increase mileage.
My daughter is likely going to try Lyle Knudson's approach to training when she is healthy.