This is pretty simple their realtor should be present to represent their clients interest and to attend to the buyers needs. You are not hosting an open house or showing the home and it’s not the buyer home yet it still belongs to the seller. So everyone needs to be respect the rights of the property owners. You need to ask them if their agent is coming and if not suggest that they call them and request their presence, especially when the arrive with family, friend, contractors and pets.
They are paying for it, and they can be there.