Negotiating advice on 30+ unit apartment complex

[Derek Caffe]

I've come across an off market 30+ unit apartment complex. My question is how should I approach negotiations when I'm speaking with the family directly? The details are outlined below.

It is currently owned by a group of family members who purchased it from their relatives in order to keep it in family. The new owners all have full time jobs and not really looking to be landlords. 

I just received an email from the head of the family group spelling out the situation and asking although they did not do an appraisal, because it was between family, what would I offer them for it. 

I've only been able to ride through the property at this point. I don't know rent roll, unit mix, market cap rates, etc.