Guardianship and witness of a fasiq (sinner)

Is the guardianship of a father, grandfather, and others permissible during nikah, if they are fasiq [1] and also is the testimony of those who are similarly impious during the marriage valid?

According to the more reasoned opinion of the Shafi'i madhhab, the guardianship of a fasiq (open sinner) during nikah, whether he be father, grandfather, uncle and the testimony of a fasiq or impious person is also considered invalid [2].

However, if fisq has become widespread and piety (adalah) has ceased to be observed, the guardianship of a fasiq or testimony of like person in marriage is permitted, as is the testimony of impious (dishonest) people in general. But the imam needs to choose witnesses who are less sinful [3].

Note:

Before solemnizing a nikah, it is recommended that an imam urge the guardian (of a fasiq) and witnesses to sincerely repent (tawbah) for their sins and renounce sins in the future.

References:

[1] A fasiq is a sinner who commits great sins such as adultery, forsaking prayers, etc. or who persists in minor sins.

[2] See: Tuhfat al muhtaj (with subcomments of Imam al Shirwani), vol. 7, p. 255 [3] See: Umdat al Mufti wal Mustafti, vol. 2, p. 128.

[3] See: Umdat al Mufti wal Mustafti, vol. 2, p. 128.