I secretly hope one of my dogs dies sooner than the other
Why do you hope for that?
One dog takes so much from me.
An older dog is hard to care of but your responsibility extends to both of your pets. It is wrong to want either of them to die.
You don't get it, he's taking too much from me and it's time for him to go.
If you truly want to get rid of your pet, then an early death should not be the solution.  If you are no longer willing or able to take care of it, you can put it up for adoption, or even just give it to the local shelter.  That way someone else can love and care for the dog.