I can’t recall the length but anything before a limit of automatically considered a handgun by the RCMP.

This is incorrect, non-restricted rifle barrels must be greater than 18.5” (18” for shotguns) and the overall length cannot be less than 26” otherwise they firearm will be classified as restricted which you have to register it under your possession and acquisition license,

Restricted - What’s included in this class

• Handguns that are not prohibited firearms

• Firearms that:

• are not prohibited firearms
• have a barrel less than 470 mmin length
• are capable of discharging centre-fire ammunition in a semi-automatic manner

• Firearms designed or adapted to be fired when reduced to a length of less than 660 mm by folding, telescoping or otherwise

It’s also worth mention while the Firearms Reference Table is not technically bound by law, the RCMP essentially treats it like it is, so no matter how much you modify a rifle it’s still technically registered as a rifle in the governments eyes.

I’m still suspicious of the PAL plus removed weapons. Is it possible they bought a gun under the table after their weapons were confiscated?

It’s important to note that non-restricted firearms are not registered to PAL licenses like how restricted firearms are (except in Quebec), the only thing noted is the transfer request between seller and buyer, currently the RCMP is claiming that neither the shooter nor mother had these firearms registered to them which can indicate these are non-restricted guns.