Haunted Mansion you get in the regular line. When you leave the stretch room you will be taken to the exit to load.
I believe Peter Pan still has a separate wheelchair line where you will be given a return time. We can't ride Peter Pan anymore because the walkway can't be stopped.
Pictures and articles I have seen recently of Haunted Mansion have shown the Fastpass Plus line going thru the line on the right side.
The Standby line was going thru the line on the left side and going thru the interactive cemetery before joining the Fastpass Plus line at the entrance to the building.
That is how it was when we went to HM in October and November.
Peter Pan had not reopened when we were there, so can't comment on that.