Get a licenced Mass. Home inspector. Contact the American Society of Home Inspectors, ASHI
website and look for an inspector in your area. We have seen plenty of unprofessional work around here in NE the last few years.
For now you need to section off the two levels. Try installing a blanket at the bottom of the stairs to keep the lower level warm. The upper level may get chilly, but will be ok since the heat will rise through the floor. If you have an attic hatch seal it off. You may have no insulation at other points also, this is why I recommend an inspection to see what to do next.