Political parties have been auditing their MLAs to ask if any of their family members are beneficiaries in the RHI scheme.
The Ulster Unionist Party has said an aunt and uncle of its Mid-Ulster MLA Sandra Overend have a business which is a recipient under the RHI scheme.
DUP MLA Carla Lockhart has indicated that her sister-in-law’s husband is a farmer and is in the scheme.
The party said Ms Lockhart “has only recently become aware of this.”
DUP MLA William Irwin has a son-in-law who is a farmer and is in the scheme.
The wife of former Ulster Unionist MLA Neil Somerville has a wood pellet boiler under the scheme in a family business, Clogher Valley Horses Welcome.
There is no suggestion that any of the relations of Ms Lockhart, Mrs Overend, Mr Irwin or Mr Somerville operate the boilers inappropriately.
The Renewable Heat Incentive scheme was intended to increase the creation of heat from renewable sources.
However, businesses were receiving more in subsidies than they were paying for renewable fuel and the scheme became majorly oversubscribed.
The fallout from the scandal surrounding the scheme, which is approximately £490m over budget, resulted in the collapse of Stormont’s institutions and the calling of snap elections on 2 March.
The UUP said it is contacting a small number of councillors by the end of the day who failed to respond to a request asking them if they benefited directly from the RHI scheme.
A spokesman for the Ulster Unionist Party said: “We are aware that many who applied to the RHI scheme feel they are being unfairly vilified because of a catastrophic failure with the Department of Enterprise Trade & Investment.
“Given Mr Somerville served however briefly as a MLA, we call on Ofgem to fast track an audit of his boiler alongside those belonging to relatives of elected representatives. That is only fair, and the best way to ensure public confidence.”
The DUP said neither Ms Lockhart nor Mr Irwin “was involved in lobbying for these individuals (their family members) and neither has any financial or other interests in the farms concerned.
“We would again want to point out that in the main those in the non domestic RHI scheme applied absolutely legitimately to what was a government approved scheme and should be viewed as such.”