Me and 4 others planned on living in a house near our University. We paid security deposit and landlord said he would email us all a copy of the lease and we would individually sign it and mail it to him along with a check for 1st months rent. Only 2 of us were to move in on the day of the start of the lease. The landlord was to come do a walk through with us and collect both of our leases and checks at the house. He never showed up and never got 2 of the leases. He went on vacation for 2 weeks and left no contact information.

The basement was such a disaster (mold, broken walls, no furnace hooked up, broken windows, water all over the floor from rain) we were advised not to turn on the gas, therefore no hot water. There was no way to contact the landlord to tell him so the 2 of us who did not sign the lease were forced to make other living arrangements. The other people (2 of whom did sign the lease) opted to not live in the house either even though they weren't planning to move in until August.

The landlord is now suing us for unpaid rent. If I never signed the lease, can I really be sued?

I would think he would have a hard time.
Pictures when you moved in would be nice, he may say the damage was done by you?
Have seen real pieces of crap people with their chump lawyers do some weird stuff.
With 5 of you, he may experience some problems. Don't let him bully or intimidate you.