Taking over management of a property with no gas Cert for 4 years

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I have been asked to manage a property (2 flats) one occupied one unoccupied by a liquidator. I have viewed the occupied flat and there is a long list of problems with it.
No gas cert for 4 years
broken windows
Damp, from roof problems
Previously no heating for 6 months
to name just a few.
The tenants have been there for 14 years and have fixed a lot of problems themselves.
My initial feeling is to re-house them, I'm sure we can find something better for them. However, the liquidators want me to collect the rent which the tenants have put in a savings account unill they knew who to pay. Also, I'm not sure that the tenants want to move out!
The question is:
Should I collect the rent and use it to make the urgent repairs or
Should I not cllect any rent off them until the work is carried out, in this case I'm not sure how the work will be paid for!
Thank-you for reading my problem of the day!