I am assuming that Tim and Jack talked and thought it would be a great idea to pool their money and hire "one great lawyer". While it does sound more economical, it would not be in your best interest to have one lawyer. Everyone has the same goal to stay out of jail. So make sure everyone hires their own experienced criminal defense attorney. Even if you cannot afford one, you will be appointed an attorney. Appointed lawyers are just as experienced and have a duty to zealously represent you as clients. I hope this helps.
One attorney can not represent two separate people involving the same case.
Additionally if the parties are pointing fingers at each other there is no way for the trials to be joined. They have to be separated because in the same trial there can't be the pointing of fingers at the other defendants. There will be separate trial for those that are saying the same thing. Still separate attorneys for each defendant.
You realize, don't you, that according to your scenario all three are guilty of murder and it doesn't matter who killed whom?
Regardless whether it might be technically permissible for Tim and Jack to have the same lawyer, it is hard to imagine how that could possibly be a good course to follow, let alone the "best" one. I never have and never would represent two defendants in a single case, even though there are circumstances in which multiple representation might be permitted.
Would Tim and Jack be best off in a joint trial (with each other, but sepatate from Bob, as I understand your suggestion)? Of course, the choice is not up to them. The prosecutor has a say in that, and the decision lies with the judge. Whether it would be permissible is a more complicated question than I would try to answer on a forum like this, and whether it would be desireable from the point of view of either of these two defendants would depend on the details of the anticipated evidence in the case.
But remember the basic problem. If these three gentlemen are "committing a robbery together and two people are killed" then Tim, Bob and Jack are all three of them guilty of murder and it doesn't matter a damn who pulled the trigger. A defense that says, "I was part of the robbery but the other fellow did the killing" is simply an incompetent defense unless the only goal is to avoid a death sentence, which is not an issue under current Illinois law.
You've asked this questions multiple times. It reads like a homework question.
It's felony murder - all three are guilty regardless of who actually did the killing.
Each should be represented by their own attorney for the best results.
Regardless, each is guilty of felony murder and each will be subject to criminal sanctions for the murder and the robbery.
It would be best if Tim, Bob, and Jack didn't rob anyone or murder anyone.