This is a very complex one, and there's no straight answer, I'm afraid.
The Land and Conveyancing Law Reform Act, 2009 abolished the life estate as a legal title, vesting legal title in the trustees. Who the trustees are should be set out in the original settlement that created the life estate, but may not be, or the trustees may be deceased. If there are no trustees, then the 2009 Act sets out who can act as trustee - ultimately they may need to be appointed by the Courts. There must be at least 2 trustees to sell the property while your father is still living.
You may, or may not be able to sell the property but there are significant legal and technical issues to deal with before you consider whether selling is in your fathers best interest (your role as attorney), or whether the sale is for your benefit.
Get legal advice from a solicitor familiar with this area of law.