I would go with separate devices. You can add a button with two set of terminals to trigger both the traditional chime and IOT thingy on the same time. Personally I don’t see the appeal on video/audio with a doorbell, but I’d guess there’s some raspberry pi project around to achieve what you want. SIP just for a single house doorbell at a first glance sounds like a massive overkill, camera with a two-way audio, possibly integrated to home assistant, works equally well without the overhead of running a whole IP telephone system with it.