Is the marriage contract considered valid if one of the two witnesses does not pray, knowing that the bride's father and another religious witness are present?

Since your father was present and the second witness, and his presence with the other witness is sufficient for the validity of the marriage. Our jurists have stipulated the acceptance of a father's testimony for his son's marriage contract, and this is what Sheikh Ibn Uthaymeen preferred. Accordingly, your marriage is valid with the testimony of your father and the other righteous man, especially since the testimony of everyone present at the contract who is fit to testify is accepted, even if they were not explicitly asked to be witnesses.