We opted to DIY invites and are not using an inner envelope to be environmentally friendly. How should we address the envelope if, for example, we have a family with 3 older children still at home and 2 of them have guests that we would also like to invite? I know it wouldn't be mr and mrs john doe and family and guests, but how would be the best method? Verbally relaying to them they can bring their bf/gf? Thanks in advance for any help!