Is it 6 dedicated units? If they weren't STR, could each of the 6 units be rented LTR? If so, this would be considered a commercial property and a commercial appraisal would be ordered by your lender (confirm this with your lender to be sure). The appraisal will take into consideration the financials of the property, as well as the replacement cost and local sales data.
Start your analysis by getting as much finanical data from the sellers as possible - P&Ls, tax returns, booking reports - for at least 3 years. Look at the expenses - are there management costs included? Other discretionary spending?
Try to boil everything down to get a true operating NOI for the past 3 years. 2020-21 numbers are going to be inflated, so take that into consideration. Once you have a solid base NOI, figure out a cap rate to put on it. Around here, a turn-key hospitality property (without third-party management in place) will trade around 10-11%.
Good luck