Thanks for chiming in, @hugh_sun! Let's keep the conversation going here for now and we can file issues as we identify code changes that would be helpful.
When you load the Submissions table, you should only get the root table fields. Did you access the connector by clicking on the link @hugh_sun shared above? When you configured each data set, did you see a dropdown with each available table? See the screenshot here for what you should see. I want to make sure you're using the latest version.
It sounds like you have a parent household table and a child table that represents people. You'd like to get a total count of all people across all households, is that right? Have you tried to do a count (NOT count distinct) on any field in the child table (e.g. name)? My understanding is that as long as each row is unique that should work.
For working with repeats, you'll probably also be interested in looking into blended data (Google reference, useful article).
I think you can do what you need with what the connector does today. However, it would be useful to have the familiar KEY available through the connector. I've filed an issue at https://github.com/UDub-Impact/OData-Connector/issues/21.