I agree with Aimeedyan. Resort guests are allowed to have visitors as long as they provide the name and room number of the person they're visiting. If by the rare chance the gate attendant turns them away, they can park at the TTC and monorail over, although I doubt they would ever need to do this.
Technically, they're not allowed to be in any of the pool areas if they are not a resort guest. But the best thing you could do is to ask the front desk for permission for your family to join you in the cabana. Explain to the desk where they're coming from too.