Jeanette, I wonder if you asking whether it is necessary to be a manager of every one of your ancestors in order to take advantage of Geni. If that's your question, the answer is No.
In fact, we have a lot of wasted effort on Geni from people creating duplicate trees in order to become one of the official managers. Since anyone can contribute to any public profile being a manager is relatively meaningless. It's much more efficient to follow the profiles that interest you, and to contribute through public discussions.
On the other hand, if you are distressed that you have to share management of your ancestors with other descendants, you might want to think about whether Geni is the right platform for your genealogy. Geni is a site for collaborative genealogy. It's strength is that many descendants can all contribute the information they have so that the tree is better for everyone. On Geni, your ancestors don't belong only to you but also to all other descendants. If you need to have total control, you'd be happier with a platform like My Heritage.