Beatrice and Eugenie will just have a Miss or Master as children like Zara & Peter, so they can call them anything they want.
There would be a weight of expectation on a future Princess Victoria, just because of the name, same as a Princess Diana.
I think Harry & Meghan’s kids will be Viscount / Lord / Lady like Sophie & Edward’s children. Unless Kate pops out one more, Louis is the last Prince of this current generation.