What is the ruling on taking clothes or money from a brother whose source of wealth is unknown and suspected of being unlawful, and does the one who takes it, along with his family, bear sin for that?

The fundamental principle for a Muslim is to seek what is lawful (halal). One should not harbor ill thoughts about another's wealth without a legitimate Sharia-compliant reason, based on the Almighty's saying: "O you who have believed, avoid much [negative] assumption. Indeed, some assumption is sin," and the Hadith: "Beware of suspicion, for suspicion is the falsest of speech." Merely not knowing the source of income does not permit doubt or ill thoughts, nor does it prohibit dealing with the person or accepting their gift. If there is a legitimate reason for suspicion, the default is to permit dealing with them and accepting their gift. The gate of piety (wara') is wide, but mere suspicion does not render something forbidden.