Brendon, tell them that the reason IoT devices won't connect is substandard network parts used in said devices AND oudated or substandard security measures.
Tell them that if you make changes to allow those devices on the network, every kid on the block will be able to 'hack' into their network, steal their data or use it for illegal stuff.
Ask them if they want to sign a release form acknowledging the risks.
Otherwise, offer to set up separate AP network that's separate and lockdown to only those devices.