Were you looking for a free solution?
Here's some ideas, but I don't think these apps connect to your homegroup but rather individual PCs.
There's this app: https://play.google.com/store/apps/details?id=com.splashtop.remote.pad.v2
It's free for basic features, but requires a subscription to stream from your PC to Android over the Internet.
I've used the free version before to stream within my LAN and it works great, it's your PC is running on your phone.
This app works well too: https://play.google.com/store/apps/details?id=com.nityaalabs.airstream
I've only ever used it within LAN and it runs great. It has PC to Android over internet functionality currently in Beta. I'm not sure if it's free to use the web streaming service though.