I think you are correct HA can’t determine who the message is for, I would have thought the tasmota sw would allow for more than one mqtt message channel 
, the reason that it always stays off is probably related HA can’t know what pir is sending the message. In theory it should work as the payloads are different, if it’s a warning I wouldn’t worry about it, if it’s an error I’m not sure what you can do about it. Have you had a look at Dr.Zzzzs video on the subject https://livetamsu.site/talkvideo/Ega4U1KRlso/sonoff-rf-bridge-w-mqtt-home-assistant ?