How so? James at 18 has the right to be HRH Prince James of Wessex (or Ed depending on fate). If he chose to be HRH Prince James, his children would be HRH. Other than that it's just the Dumpster Fire and William who would be able to pass it down. That's not a lot.
HRH isn't hereditary. The current LPs limit HRH to the children of a sovereign, the grandchildren of a sovereign, and the children of the eldest living son of the Prince of Wales...James's children will, regardless of his style, be great-grandchildren of a sovereign and therefore will not have an HRH. Regardless of what James does his eldest son will one day be His Grace The Duke of Edinburgh if all goes to plan or The Right Honourable The Earl of Wessex if things don't. Much like how none of the children of the current Dukes of Kent and Gloucester and of Prince Michael of Kent have HRH as while the princes are grandchildren of GV their children are great-grandchildren of GV.
Archie and Lili will, if all goes well, one day be grandchildren of a sovereign and therefore under current LPs automatically HRH. Archie's children as male-line great-grandchildren will not and instead his eldest son will one day be His Grace The Duke of Sussex.
George and Louis's children will, if all goes well, one day be grandchildren of a sovereign and therefore under current LPs automatically HRH but Louis's grandchildren will be male-line great-grandchildren so they won't.
Lili and Charlotte's children will currently be nothing since they're girls and there's currently no gender equality...much like how Peter, Zara, August, and Sienna have no titles or styles regardless of their degree of relation to a sovereign.
Though like I said limiting titles is largely a PR exercise without addressing the bigger issues...lack of consistency, need for gender equality, and need to stop connecting titles and working status as titles are only meant to indicate degree of relation.