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It may be aphids or a similar pest. You can treat the plants with a pesticide. As they are food plants, I like neem oil as it is organic, safe for people and beneficial bugs and effective on pests. This article may also be helpful: https://www.gardeningknowhow.com/plant-problems/pests/homemade-aphid-control-a-natural-way-to-kill-aphids.htm

Sounds like a fungus, possible from too much moisture or even pests. Remove infected leaves and treat the plant with neem oil. Here is more information: https://www.gardeningknowhow.com/problems/pests/neem-oil-uses.htm, https://www.gardeningknowhow.com/edible/herbs/basil/basil-diseases.htm, https://www.gardeningknowhow.com/edible/herbs/basil/how-to-grow-basil-plants.htm

Since peppermint is in the mint family, it is a spreader with the likelihood of taking over surrounding plants/areas. Therefore, I would recommend planting the peppermint in a container (which can also be bottomless and sunk into the ground) to avoid this problem. As long the this plant is contained, then planting the others nearby should be ok, but I would not recommend planting them together in the same pot.

Just clip the plant back to encourage side growth and fullness.

They need some nutrients. Give them some water soluble fertilizer at half strength.

Try adding a bit more nitrogen-rich fertilizer and see if this helps with the greening up of the foliage. If not, it may just be the type of basil you have and is no indication of there being anything wrong as long as it appears healthy otherwise.