I suspect bacterial infection. The very first thing you must do is move the diseased plants away from all your plants, and at a minimum the two Tulsi plants that are still healthy. If they came from the same lot, you will be lucky if they survive.
If you used the same soil, or if they all germinated from the same set of seeds, you should also separate the two healthy Tulsi plants from the rest of your other plants.
Discard the 5 and do not reuse the soil or pots without sterilization. Do not throw in a compost pile either.
If you tell us more about how or where they were purchased/germinated, we may be able to help better. Can you try to get us clearer close-ups of the leaves, if possible?