Unless there is something unusual about the property it should be worth the potential cash flow divided by an appropriate discount rate for the area. If you are a buy and hold investor the discount rate is determined by the return you want on the investment.
I would probably start out finding out the rental rates. Usually I use an 8% discount rate and a 50% expense ratio. For instance, $700 per month for each unit is $50,400. Using a 50% expense ratio you get $25,200. At a discount rate of 8% you get a value of $315,000.
I would look to see if there is deferred maintenance. This would be subtracted from the above number. Later on you can look at actual expenses and get a better value.
The restaurant is a problem because the owners have not been able to find a permanent renter at the price being charged. That could indicate that the rent is too high or that the property is not in a good location for a restaurant. Is there another use for the property? I don't want to use an 8% discount rate for "maybe" income. I would probably use 16%.
I hope that all 6 owners agree that the property should be sold. Even then, they might not agree on the price. Good Luck.
Bill