Blockage between toilet & main line

I'm helping a friend try to unclog a toilet line. The main sewer line appears to be clear - we can auger from the back yard all the way to the front of the house. (and the toilet at the front of the house operates fine). However, the toilet & shower in the main bathroom do not drain. The toilet has been removed - there is water standing in the drain pipe. We have tried running a hand-powered auger down the drain, but are unable to reach the clog (it feels as though we are reaching a turn in the pipe). We are unable to reach the clog from the main sewer line, because the auger needs to turn to head toward the clog. We have also tried dumping a large quantity of water into the toilet via bucket, and plunging.

What steps can we take to resolve this? This has been a continual problem ever since my friend took possession of the house. Will a power auger be able to navigate the turns necessary to reach the obstruction?

The house is on a slab foundation and is approximately 40 years old.

Thank you for any advice you can provide.

From Toilet Opening

You should be able to clear the line by running the sewer machine in from the toilet opening. If you have an open reel machine you will need to cover the walls with pastic.