The english wiki is not that clear, although it seems like it is a direct translation for most of it.
https://de.wikipedia.org/wiki/Eroberung_von_Philadelphia https://en.wikipedia.org/wiki/Fall_of_Philadelphia
Now i was wondering if those two byzantines were actually enemies but forced to fight for the same side. Since everything else i find about those two guys does not seem to imply that.
Anyways, i would be happy to have some more information about the siege/fall of philadelphia.
If anyone could shed some light on this, i would be grateful
according to the book "Wörterbuch der Schlachten, Belagerungen und Treffen aller Völker" by Franz Georg Friedrich von Kausler, written in 1833 that is exactly what happened. (Google has the book in its archive, but only in German and it might be difficult to read if you're not familiar with the Gothic Alphabet)
In this book he states than Byzantine historians noted that the 2 Emperors joined Bayezid I and were "amongst the first to climb the city walls" when the city refused to surrender to Bayezid who it considered to be a "barbarian".