I wouldn't say grandmother was a lesbian or obsessed or anything of the like, she was enraptured. Mama-Iris charmed her, and that charming made youngrandmother covet mama-Iris. Now, as humans, when we covet another person we do tend to want skinship with said person; which could be construed as lesbian. However, I doubt her gender had anything to do with it.
This is why grandmother doesn't covet Iris, she's not gay for her. She just thinks that Iris, having the beauty of her mother, deserves to be in the Royal line. Perhaps maybe she wants her line to have their bloods mixed together? It would mean the same thing, in the grand scheme.
Also, glad to see the other royals notice Dead-Ed and his Trollop are rather bullshit. But, somehow he holds more royal authority than the first prince? I'm not sure why. Unless the King decreed something to the effect.