You can follow these steps to add Facebook Page to Google Sites.
#Option 1. Use Facebook Plugin
#1. First, access this URL
#2. Paste your Facebook Page
#3. Get code
#4. Copy both Codes
#5. You can add it to Google Sites via Embed Feature.
#6 . Paste codes to embed code box
#7 . Result
#Option 2. Use 3rd party Tool
With this free tool (choose free version is enough), you can customize much more than using Facebook Plugin.
#1. First, access this free tool and click Create widget for free
#2. Choose Facebook page layout and click Continue with this template .
#3. Next, connect to your Facebook Page
You can also set layout, style here then click Add to website for free.
#4. Next, Click Publish on top right
#5. Choose Free Plan and click Copy Code .
#6. You can add it to Google Sites via Embed Feature.
#7. Paste your embed code
#8. Click Insert
#9. Result
