Hi @ournev
The following what I will say is only my own views.

I would like to ask the question "can I use b2evolution to host a tree containing photos, documents,and the odd short video, maybe as a manual entity".

As you said, it's maybe a manual entity. We can build the family tree by using categoris which have inherited structure.Under each category, we create several articles, each article as a member of the family.
At the same time, we use the plugin of 'Auto Links'. Once we have created the member article, input the member name and corresponding article url into 'Custom autolink definitions' form. Then wherever we type the member name, it will show the member link automaticly.

My site will contain other items apart from the tree and is intended as a family focus point.

Yes, we can also create other collections for richly displaying content. For example, a blog collection to show the big event, a photo collection to show the precious pictures, a forum collection for family disscution.

Thanks Haharen I will give it a go.

@ournev
You're welcome.