@Andrew Syrios Thanks for your advice. I agree. We have the clause on our lease: It is required to maintain the temperature at 50 degrees Fahrenheit at all times.
@Jimmy Klein Thanks for your advice. We will provide some compensation for downstairs tenants and hope to get some recoup from upstairs tenants. But I have to agree with some other landlords about following the temperature requirements clearly written on the lease. Upstairs tenants clearly neglected this point.
@Moshe Aharoni Thanks for your advice. I agree with some of your points, but we don't like to have any law suit going on... We just want to keep the matter as simple as possible. What we are looking at is it seems that only upstairs tenants need to go through their Renter's Insurance if they decide to since they have to pay for some damages they caused (they may choose not to depending on their deductible etc.) As to downstairs tenants, they don't seem to go through their Renter's Insurance since their are not the ones who caused this incident.