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It could simply be suffering from over watering. Rather than watering the plant every day, you should be allowing the soil to dry out some before giving it more. Too much water can lead to fungal issues and root rot. These articles should help: https://www.gardeningknowhow.com/edible/herbs/sage/growing-sage-plant-indoors.htm, https://www.gardeningknowhow.com/plant-problems/environmental/signs-of-plants-affected-by-too-much-water.htm, https://www.gardeningknowhow.com/plant-problems/disease/treating-root-rot-gardening-tips-for-housplants.htm

They may be damping off (which is caused by a fungus) or root rot if they were over watered. Make sure the drainage is good and add some fungicide to the soil to keep off the fungus.

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.