Ok so i went an bought my O's 4 months ago now ( maybe 3 )
and Kits is HUGE and i mean HUGE , Where Applelay is VERY VERY tiny , They both get the same amount of food , cause they will eat from my hand .. Apple isnt growing , and i DO not understand , we tried to think maybe one was male and one was female but we are lost , i never seen this at all

Also i was playing with them a couple days ago ( yes i play with my fish lol ) and Kits has red marks on his mouth
they still have not gone away and i am not sure what it could be from either ,

Can anyone please help me

Can you post a pic of the red marks so we can help you with what it is

Oscars will grow at different rates. Once one gets a little bigger it will have a bigger belly and eat more and will grow even quicker. Males and females grow at the same rate and will be the same size when full sized

I suspect your small oscar has grown but you just havent noticed it. The bigger one has just grown more. Try taking a pic of them against an object in the tank and compare it with another taken 2 months later. when you see your fish everyday you dont notice the growth of each fish but you do notice the growth of the fish when compared to each other so it can look like one isnt growing and one is

It may be there is something wrong with the little one which is why a pic would be helpful