Great! (Well, not that you have aphids, but...).
I would have expected to see more, but at least you found something. In the absence of sticky honeydew, I still suspect a second culprit. You can try rinsing off the aphids with water. Outside unless it's freezing, or maybe over the kitchen sink. Basil leaves are so delicate that sometimes a strong spray bruises them. Insecticidal soap is another option. Or a new plant if you're not passionately bonded to these.
As for your other plants, careful inspection is the best plan. Good luck
