6plex on r4 zoning not sure if it’s all legal or if I could be gr

[Lane Koehn]

So I’ve been cold calling and found a owner Who wants to sell a 6plex plus a single family house on a r4 zoned lot. The house cannot be separated from the multi family lot he says ...my question is what about the r4 zoning with a 6 plex on it? He has a full basement underneath that they have started framing in more apartments but quit before they ever got them finished. I’m new to this and need some advice! I don’t know the age of the building yet, but I believe it’s 1970-80ish? Could’ve it been built before the zoning changed to r4?perhaps it’s grandfathered in? Thanks in advance for any pointers!