OK, so when I play multiplayer with my cousin I can sharp aim until he moves then my yellow dot aimer thing goes back to my guy.. He has no problem with this though.. it wasn't such a big deal, but now we started going agents each other and its incredibly annoying not being able to pick of his guys like he does mine..

anyone have this problem.. or might know how to fix it? (I use keyboard/mouse, and he uses a USB controller)

No fix, known problem.

both use keyboard and assign sharpaim to something inaccessible.

I think some keyboards have limitations on how many keys you can press at once, and other keys seem to have a higher priority than others. I have an extra USB keyboard to get around this problem.