Start with constraints everyone will actually follow
Ask each traveler for one thing they would like to do and one thing that would make the weekend difficult. Record fixed constraints separately: check-in, the journey home, any booked admission, and the time someone usually needs a break. A child who dislikes long walks and an adult who wants several museums are not problems to average into a vague moderate pace. They are concrete inputs for choosing a shorter route and an optional split activity.
Give each day one anchor experience and one optional extra. Write down who can stay with the children if adults split up, where everyone will reunite and how they will contact each other. Keep the shared version simple enough that another adult can use it without reading a long message thread. No activity should depend on information stored only on one person's phone.