scortch on leaves on two plants and left drop on another plant
I have house plants. Two of them have suffered scortch on the tip of the leaves. The edges then become yellow and eventually the leaf is black all over and shrivels up. It does not drop but stays on the stem. The plant at one time flowered, but now it is slowly dieing. As the leaves die as described before. The other plant has yellow spots. the spots eventually spread all over the leaf and then it drops from the stem. Both plants are 7-8 years old. the plants are in potting soil, which is a mixture of soil over the years. The soil has never been fertilized. The soil may have been contaminated as my cats may have used it as a place to uninate without my knowledge. In the spring, summer and fall the plants are outside on the side porch. There is not evidence of insect damage.
We actually think your plants look pretty good. It's not uncommon for some older leaves to brown and die. It could be bacterial, or even if the cat 'sprayed' the leaves, it could produce a burned look. Simply trim out those leaves.
The one with the yellow spots is a type of croton and it is normal. Actually, there are many varieties, and even one that has yellow and red and green leaves, all on the same plant.
Both of these plants would be happy with some houseplant fertilizer every two weeks during the growing season or once you put them on the porch.