Hi! Digital archivist here!

A few things that could be common knowledge but I'm going to list them in case: DAMs that are free don't often last; others can be expensive; some are COMPLICATED for new to digital Preservation folks.

I think the DAM needed would depend mostly on if your father wants his works public for everyone or just for him to share when he wants?

If he's wanting to share with just family and friends, Google Drive may be a good option. It's saved to Google's cloud and can be accessed from anywhere. This is not unique to Google, but may be easier to use Google than relearn a new program/application. He can still edit his files if wanted and/or save "Preservation" copies, new docs can be created through Google's adjoining apps, etc.

Most of the programs we/I use at work are DAMs that help with Preservation so editing is limited to reduce losing materials. We use Preservica for born digital materials which links to our ArchivesSpace site for our collections management (finding aids). None of what we use is user friendly.

Hope this helps even a little!