SenecaFalls
The Earl and Countess of Wessex accepted their titles on marriage, but still use Lord and Lady for their children, rather than the Prince/Princess titles they would be able to use.
I think the difference for the D and D of Sussex is that Harry is not the son of a reigning Monarch (as Edward is), so their children are not entitled to the Prince/Princess under current rules. When Charles is on the throne (if), I think this changes.