The two companions, the dark elf and the drunk. I was on my way to Mor Khazoul (Spelled it wrong) the Orc stronghold West of Solitude, while riding you have to ride through a narrow track, there were bandits their so I decide to take a shot and realise it was Athis so I carried on. Later when I got back to Whiterun I went to Jorvassker and they both attacked me. They were then killed by the others. Then while in Riften I get two letters of inheritance.

Isnt tolfdir the guy in the college of winterhold?

You probably mean Torvar. The Companions go out on missions in the countryside- they're not bandits. Obviously they turned hostile because you attacked them. This can also happen if they pick up friendly fire from your companion.

Personally I've found the companions highly intolerant to friendly fire. One stray arrow and they try to kill you, even after all you have been through together :'(