Rental properties

I got an offer to buy 4 rentals that have a cash flow of 2554 a month. The asking price is at tax value, which is between 150k -200k. They are all owened by the family, and they just want to sell them since mom has passed. After talking to them I think a low offer might get it.
I'm not sure what to do now, it's not listed with a realtor, and I don't have an investor to partner with to have a second look to see if it really is a great deal.