Should I tell my oldest son he is his younger brothers father?er brothers father?

will it change anything now for the better or will it cause ill feeling and trouble ?

I'm sure in his mind, he already knows. How do you think he will react with your confirmation of this? How do you think your youngest son will react if he knows his brother is actually his father?
Are you wanting to start that sexual relationship back up? If not, let it go.

Who does that telling serve? You? Your son? His son/brother? If it's about you clearing your conscience or something like that, then I think you should keep it to yourself. Why upset everyone else with this knowledge? If there's some compelling reason you do it, like genetic medical conditions that need to be disclosed, then, were it me, I'd talk only with your son and let him decide what to do about it from there. I get that this isn't the most honest approach, but blowing up a family is a very big risk to take. Don't you think?

Since you were having sex with two men how do you know which one is you baby's daddy?

If he would be upset, I suggest you not tell anyone.

Nothing good can come from telling him: leave it be

Would it serve a purpose