Welcome to Gaia! ::

my cats have been getting a little overweight recently.
Not like super obese but just a little chubby.
I don't know if I am overfeeding them or there just getting ready to grow.
Can anyone help me?

most of the time if you are going by the amounts according to the bag of food what you feed them it is still too much. you should ask your vet next time you go and they could tell you about how much your kitties need. or they could need more exercise

At this age, the growing slows a lot, and with it the metabolism. You need to cut back on portions. No more than 1/2 cup per day including any treats or table scraps.

Free feeding can be problematic in cats with weight problems. It's preferable to feed 2-3 small meals a day so they aren't over eating.

Also, if possible, a higher quality food would do a world of good. Meow Mix is not a balanced diet. If you must get a cheap grocery store food, at least aim for something made by Purina. Purina Pro Plan for example has stable formula's. Or aim for something with the least amount of grains and by-products with a named meat meal as the first ingredient.