Regarding the Sussexes, the source indicates that both Harry and Markle are part of the complete plan — from the original announcement to the procession and interment.
Harry is anticipated to stride alongside his brother, who will become king, leading the procession from Westminster Abbey through the streets of London.

The Sussexes will be invited to join the family vigil throughout the lying-in-state time at Westminster Hall.
Additionally, it has been reported that plans have been created for Prince Archie, 6, and Princess Lilibet, 4, to be present at the funeral service along with their parents.
Although most state funerals — referred to as Operation Menai Bridge for Charles — usually adhere to tradition, every monarch has the ability to implement various modifications to the arrangements.
Insiders suggest that for Charles, the service will highlight his lifelong commitment to the environment and incorporate sustainable features whenever feasible.
It is also reported that the time of royal mourning will be shortened to align with the duration of national mourning.