Is it permissible to give money instead of abayas, with the possibility that it might be used to buy immodest abayas or clothes?

There is no harm in gifting money to the aforementioned women, and the possibility of them purchasing unlawful things with it does not prevent the gift, unless you are certain of it. In this case, strong presumption is equivalent to certainty, and this is a fundamental principle in Islamic rulings, as stated by Al-Alawi, Al-Shatibi, Al-Jassas, and Al-Muqri. This is supported by the Almighty’s saying: "Then if you ascertain that they are believers," and the agreed-upon Hadith (definition) of Umm Salamah: "So I think he is truthful."