Is it permissible for a girl's paternal uncle to marry her and her sister off without their father's knowledge or permission?

If the father appoints the paternal uncle to marry off his two daughters, then the marriage is valid if the remaining conditions are met, and the father's knowledge or absence is not a requirement. Agency in marriage is permissible, whether the guardian is present or absent, whether he is a mujbir (one who can compel marriage) or not, and the agency is absolutely valid and not restricted to a specific suitor. The agent of the guardian must meet the same conditions as the guardian: justice, maturity, masculinity, puberty, sanity, and unity of religion. However, if the father did not appoint the uncle as agent, then the marriage is invalid according to the majority of scholars.