Seems like a fun project but couldn’t you do the same thing easily with a shared combined calendar and a tablet of your choice displaying said calendar?
You are over-engineering this concept. A simple shared calendar absolutely would work. If you want more features, go for it, but that doesn't mean a shared calendar is a non-functional solution.
Some stuff you want in agenda-format (next 5 events on the calendar), others you want in a monthly view, others in daily or weekly.
And then you have alerts, weather etc that doesn't really fit the calendar format that well.