Question about roommates, leases, and evictions - Dupage Co, IL

So without trying to get too much into this and start ranting about roommates - I rent a townhome with 2 others in DuPage county, and as of this weekend, one of my roommates has started getting very hostile and texting what I've taken as pretty serious threats toward my other roommate and I: both toward ourselves and our property.

I've avoided any significant response because I'm not sure what my legal rights and protections are in this regard.

It's becoming apparent that he has to leave, but I'm not sure what that process looks like. All 3 of our names are on the lease with no primary lessee of any kind.

I'm not sure if it changes anything at all, but this tenant was just added to the lease in September 2017, while I've been a tenant since September 2012.

I'm assuming I'd have to go through my landlord for any actual evictions, but even if I were just to ask him to leave - or if he chose to leave on his own accord - what happens with the lease? Is he still financially responsible for his portion? If he ends up evicted, is he still responsible? If not, what happens to his financial portion of the rent? Would that end up falling on the other roommate and I fully?

Are threats even a serious enough legal ground to stand on for requesting any king of eviction?

Also, our lease ends May 15th... would that process take too long to even be worth it?