I would recommend having a moleman in the group. Keeping one teamed up near Marcus makes it a real pain for the other crew to kill him, not to mention molemen can actually hit fairly hard. Just make sure you don't charge Marcus too far ahead so that he is out of range of sluffing off the damage to the moleman.
Hoarcats can be fairly effective with the amount of damage that they can do, not to mention the ability to sacrifice height 2 models when running in packs. Their only real downfall is they are not the fastest of models.
Remember the snakes are incredibly fast, so you can get them across the board very quickly and tie things up. And don't underestimate the power of Terrify. It can mess up some of the most well laid plans.