Is sending money transfers through someone who sells alcohol in Yemen forbidden (haram) or is it a matter of doubt (shubah)?

There is no objection to dealing with a person who sends remittances to your family through him, especially if no one else is available. The Prophet, may Allah bless him and grant him peace, traded with the Jews despite their consumption of usury and unlawful gain, and he bought from them, and he died while his shield was mortgaged with them. Some Companions also worked for them for a wage. There is no objection to dealing with this person even if some of his earnings are unlawful, and a fatwa has been issued previously permitting dealing with mixed wealth.