Question re 6-wheeled trucks/bogies

[Puddlejumper]

I don't know about CNR coaches specifically but the Athearn coach is a generic model and has 6 wheel trucks no matter what RR name is on it. Most of the coaches I have ever seen had 4 wheel trucks, while the heavier diners, pullmans, etc. had 6 wheel trucks. I probably would change to 4 wheel trucks, but if you want to keep these trucks there is certainly nothing wrong with experimenting with removing one of the axles. I would not remove the axle closest to the coupler due to the bolster location on the truck, I think you would be inviting more derailments. I would remove either the center axle or the one furthest from the coupler. I really don't think body mounting the couplers will be of any help on these sharp curves. The truck mounted couplers will stay lined up on the centerline of the track whereas the body mounted couplers will swing way outside the railhead and could complicate your current derailment situation, unless you go with complicated swinging draft gear.
I don't know your level of experience, if you feel confident making those type of modifications that's great. For a beginning modeler I would recommend swapping to 4 wheel trucks and leaving the couplers on the trucks.

Dave