我该怎麽办

we have a project. I finished my part and now hand it downstream for other groups. there are two groups(lets use group A and group B) to take over it. what happen following is group A take over and do it and when they finish, hand it over to group B. but group B leader want me to continue the work which suppose to be done by group A because I do better than the person from group A. then the product will be easier to handle for group B
I don't want to do it because 1)I don't want to upset group A people. 2) I am not interested at doing it. I would rather spend my time on something else.
but I don't want to upset the group B leader too.
How do I untangle this problem? Thanks for any input.