I totally agree with everyone here, what one gets to do all gets to do. True that the OEM will get big and take up more room, but it seems like all giant dogs have no idea about how big they are, they love to be "lap dogs" sit on you, or sit on the couch, it must be very confusing for your oem to see the little one be allowed on the couch, but not be able to get on there.
They are like kids and since human kids can talk (or shout hehe) I know for a fact that if they for a second think they are being unfairly treated, that one gets to do something the others dont, well they feel very hurt and confused and at least mine dont hesitate to tell me lol..... So I am sure dogs feel that way too.
We were in a similar situation once, well my ex and I were. we had danes and a min. schnauzer he thought it was okay with Happy on couch and bed (schnauzer) but also thought that Hanna and Zorro could stay on the floor. We had discussions and even arguments about it, but well to make long story short, I refused to treat our dogs different so they all ended up in couch and bed. My dogs have always been as my children, and I think I may have said something like "if you dont like them in couch or bed, you can sit and also sleep on the floor" I dont recommend you to tell your wife that hehe but try and explain to her why it is not fair and that your oem is probably wondering why he isnt allowed to do things the little dog is.
Marit