Google+ Checkvist community posts 2013-2018

My list-style is set to Checkboxes. But checkboxes only appear for lines that have NO children. Is that by design?? I can't "complete" a task if it has any children? It sounds related to the setting " Close parent task when the last child is closed", which i have set to Off.  i just want every line to have its own status of completion, regardless of having a child or not, and regardless of a child's status. Is that possible?

I am confused about sharing. I have a Pro account, and I want to use Checkvist to manage projects for many different clients. Each project would have one list, and I want to share only that list with the appropriate client. -  Do all my clients need a Pro account too? Or can they have a Free account? -  Would my clients signup for their own account, entirely separate from mine (except that we share a list)? Or would all my clients need to be "on my team", somehow as sub-accounts within my master account? I do NOT want all clients to have access to all my Lists.