That worked! Thank you, Zaimat! I had noticed the word, "Engage" above the sector but I never realized it was a button. An "Attack" order in the Order's menu would be more intuitive and would allow you to choose which planet to attack. In the case of these sectors, there were friendlies in there two that I wished NOT to attack.
The reason it's not an order is that you "Engage" combat with all your forces in the system. Putting in on the order list would indicate specific to that single task force.
Engaging won't result into combat with friendlies unless you specifically select them on the combat prompt and also manually select to fire on them. The Auto AI won't attack neutrals or friendlies.