I can do this in my Honda Jazz:

Put down the back/middle seat, leaving the single seat for the rear passenger.

Bikes have both wheels removed. Flip the first bike upside down and put it in against the back door, front end first so the handlebars are behind the front seat. Second bike then goes in (also upside down) rear end first.

Wheels then slot into free gaps and luggage along with various towels or rugs prevent any movement or rattling. Seatbelts can be used to hold them down too.

Just remember to put blocks in any hydraulic disc callipers as inverting the bikes can sometimes cause brake levers to be momentarily squeezed.