So how do these injuries work? I have guys that show as "probable" but it show the injury is 3 weeks or 6 weeks or something like that?

Weeks is a estimate of when they'll be healthy. Probably, doubtful, questionable, and out are simply guideline terms referring to the percent that a player might get playing time. It's up to you to play them or bench them. Keep in mind a injured player is more likely to reinjure.

It is always best if you can let them rest. One thing to check is actual health to get an idea of severity as length of injury is not always a parallel to that extent

Thanks for the feedback. That helped!