Nothing wrong with having both Bayside and Kingston parking permit on your windscreen. I've been doing it for over a decade.
The property owner (rate payer) gets two per property in Bayside, not the resident. As a landlord you can choose to give them to your tenants or not! Renters can apply to Council, but have to prove residence etc. and pay $60 or so. Its a plastic film pressure sensitive type sticker thats designed to be removeable and reapplied (no glue).
In Kingston, they are meant to get posted to the property, and no rego is recorded etc. and meant to be for residents. If you dont get them in the post, go to the office on Nepean Hwy in Chelt, show them some docs that prove your address and they'll give you one. Its a paper based sticker with a glue face... can be removed but slow and steady so you dont rip it.
Get on it