Wow, cool!
I think this pretty much depends on the use case and size of the data. For smaller data sets I think that one global heatmap is enough. For larger data sets, I think that for each family/surname a dedicated heatmap might be cool.
I only have like 250 people. So for my use use I would like to have only a global heatmap with all events.
As it depends on the use case and size of data: Why not offer all the above possibilities (with sane defaults).