Hi Alasdair,
indeed Gramps Web could be a good option if you want to allow your family members to edit your tree. You can still synchronize it with your Desktop installation of Gramps (which is more powerful and feature complete) and use the online version for collaborative editing or (read-only) sharing.
Currently, installing Gramps Web is still not very easy. Self-hosting it requires some knowledge with docker and related tools. The easiest option at present is using the DigitalOcean “1-click app”.
We are also working on a hosted version where users can just sign up to create their Gramps Web instance (without installing it themselves), that should be ready later this year.