Fragger Level 27 is all about the second man hiding in the house. You can either leave the first man until last or you can dispose of him straight away. In the video above I decided to dispose of him once I blew up the platform in the house.
Step 1: Throw a grenade into the front entrance of the house on the second floor.
This should blow up the ledge that would otherwise stop the TNT chain reaction in the house reach the second fragger man.
Step 2: Loop a grenade over the small brick wall and take out the first guy.
Step 3: Loop a grenade over the top of the house and into the chimney. The grenade should then drop down and set off a chain reaction on the TNT boxes. You will also find that with the ledge gone from Step 1 the TNT will be able to reach the second man hiding deep within the house.