Treat these like mini-races and do a 20-30 minute dry land warm-up. You can use easy jogging that builds to Steady or riding your bike to your open water location (or pool).
To simulate Open Water in a swimming pool, see if they will let you slide 3-5 lane lines over and create a box that you can swim around – set your turns under the flags so you don’t touch the wall. Quite often a “hot dog” shaped course is a great way to learn to make turns without losing speed.
For turn buoys, we used to use floats with rubber-coated weights to hold them down.
With your “races” that start with a swim, put the slower swimmers up front (or give them a lead) – this gets everyone used to swimming in traffic at the start.
Race Format #1 (Choose One, or Mix & Match)
Race Format #2 (Drafting Decisions)
Race Format #3 (Swimming While Loaded)
End each “race day” with an endurance set such as the following:
If you are too shot to swim 2K at the end then loosen with 200 Easy.
You can complement the Aquathon workouts with a small group ride where you insert 2x20 min pace-line (sustained Threshold effort, not max effort). Total ride duration should be 60-90 minutes. Great training for short course athletes.
Watch how the fact that you had your HR up earlier changes your reactions/emotions during the ride. Learn your tendencies, as these will be magnified in a race. Make sure that your decisions are serving your goals.