I have spent thousands of dollars over the years on my Plex setup. I'd caution against the assumption that switching to Plex and hosting your media is going to be cheaper in the short run, or maybe even the long run, than paying for streaming services. Depending on your use case you may even need to pay for Plexpass. (Hardware encoding, iirc, is locked behind their Plexpass subscription.) And factor in the inevitable troubleshooting you'll have to do when something doesn't work for your brother's family.
Do the math for yourself, is all I'm saying. It's not automatically the better solution.