You can take the credit for your home, but not your parents'.
This, from the instructions for Form 5695, Residential Energy Credit:
Who Can Take the CreditYou may be able to take the credit if you made energy saving improvements to your home located in the United States in 2018.
Home.
A home is where you lived in 2018 and can include a house, houseboat, mobile home, cooperative apartment, condominium, and a manufactured home that conforms to Federal Manufactured Home Construction and Safety Standards.
You must reduce the basis of your home by the amount of any credit allowed.
You can take the credit for your home, but not your parents'.
This, from the instructions for Form 5695, Residential Energy Credit:
Who Can Take the CreditYou may be able to take the credit if you made energy saving improvements to your home located in the United States in 2018.
Home.
A home is where you lived in 2018 and can include a house, houseboat, mobile home, cooperative apartment, condominium, and a manufactured home that conforms to Federal Manufactured Home Construction and Safety Standards.
You must reduce the basis of your home by the amount of any credit allowed.