No matter how much you deny it, at one time or another all grandparents that become parents again feel this way. And it doesn't mean that you don't love the child(ren) any less.
Most grandparents are either retired or thinking about retiring. They are empty nesters...all children are grown and out of the house. It is time to relax and have some "me" time to do what they want when they want. No set schedules. Then along comes a grandchild, or grandchildren.
Suddenly their nest is full again and there are set schedules. Maybe the grandparent was going back to college and has to give it up to be there for the grandchild(ren), they have to change their work schedule to more or less hours or even a different shift, no more free time, no more sleeping in, watching what they want on television and the list goes on.
It is only natural to feel "resentment". Your whole world has suddenly turned topsy turvy and your time is no longer your own. But there is nothing wrong with feeling that way.
There is also nothing wrong with feeling anger toward the parent(s) either. Just make sure that you do not let your feelings affect the grandchild(ren).
They have no control over the situation and they are dealing with emotions and feelings of their own. Find a support group or seek counseling. Just remember, resentment is a natural feeling and nothing to be ashamed of.
Stages 
