I know this is going to be an unpopular position, but here goes. <donning flame-retardant suit>

When my wife and I travel together, we sit next to each other and we never grab aisle/window. Why? Well, first we like each other's company. But also because we figure that the inconvenience of shared space & armrests is minimized when couples sit next to each other. I can imagine reserving window/aisle (hoping the middle will be empty) and then moving if middle is taken.

But if a couple is sitting window/aisle and won't move to sit next to each other, then I assume they essentially are just in it for themselves and they don't give a crap about the comfort & convenience of others. And so I'd feel no inclination to do anything to make their flight more comfortable or convenient.