You can use Anyrail, Wintrak, etc. Some things work out fine , but others end up being just cut and try fitting. Check the double track passing clearances with long cars coupled in at least pairs in both directions. Coupler push/pull spacing is different, making the car ends swing out further. Speed can also affect passing train clearance. Make sure before you cover any area with tunnels.

I have created a reverse loop using 9 R5 and 3 R4. The end result is that the train enters on the outer track and then returns on the inner track. The track spacing should allow you to either switch tracks or join the two together using the slim switch. I have done this kind of setup frequently on my teppichbahn (floor layout) as per Swiss prototype, trains run on the left hand side.

The same can be done with 9 R4 and 3 R3 to have a tighter version of the same loop.

What I don't think can be done is to have two such return loops in parallel, as there is no switch track which would permit this.

Wintrack or SCARM should allow you to visualize this on a computer.

Regards

Mike C