Splash, isn't it "DESIROUS" of fine work? Used to be anyway... The ddesire has to be there. If it's not it's not. Say that you're praying for the desire to be increased and you're leaving it with jehovah..
Also, there's the scripture where it says that he gave SOME as evangelisers, SOME as teachers, SOME as etcetera etcetera etcetera... Not everyone NATURALLY progresses to be an elder or a CO or a member of the gb. The illustration is given of a body, each part playing a different role. Tell them "I'm perfectly happy in the role I play currently in the congregation, and if that changes in the future i'd be only too happy to let you know, but thanks for considering me anyway"
It's tough I know, when family pressures and expectations are heaped upon you, but i can tell you, the guilt goes away very quickly, and they'll soon get used to you not being the person they thought you were.
Just say no. It's not mandatory.