I've tried side loading YouTube TV onto my fire stick and I have google services side loaded using this guide from AFTVNews (sorry I can't link as I've not met forum requirments) as well but it's telling me I need to update my google services in order to use the app.
Here are the Gapps I've successfully sideloaded:
- com.google.android.gsf.login v4.4.4-1215936.apk
- com.google.android.gms v8.7.03.apk
- com.android.vending v6.0.2.apk