If you just want videos from PeerTube and Piped to appear in the same feed, you can do that via an RSS news aggregator. For example, Mozilla Thunderbird has that built in, but there’s also tons of small, dedicated applications, depending on what OS you’re using, or even as a browser extension.
In PeerTube, you can get an RSS feed, either of your subscription feed directly, or for the individual PeerTube channels, you’d like to subscribe to.
I don’t know, if you can also get an RSS feed for your subscription feed in Piped, but you can get it per channel. Just click on the little WiFi-looking button.