Bill Guthe all you have to do is create a group with shared editing capabilities and then share the items with that group.
Also keep in mind that anyone with an Administrator user role can update any content, regardless of who the owner is or group it's shared with, so this could be a potential solution as well.
Best,
Katie
“The goal is not simply to ‘work hard, play hard.’ The goal is to make our work and our play indistinguishable.”
- Simon Sinek