One suggestion I have is to work on one story at a time. If you get ideas for the second story, jot down the details but do not write the story as it will cause more confusion. Another thing you can do is do a short outline. It doesn't mean you have to stick to it but it gives you a point of reference and acts like a road map but of course you can take a detour. You should also do a character analysis and give each protagonist a different personality, family life, economics, education, etc. My suggestion is they would look different also. The same with the female lead character. Writing takes concentration and constant revision. The important thing is to get the story out on paper as you can always go back to revise. For now, concentrate on one story at a time. Hope this helps.