All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
It is better to donate for your uncle because the mosque minaret is not a confirmed matter; some scholars are of the view that it is desirable to build a minaret as it helps the sound of the Athaan reach farther and thus more people can hear it.
As regards helping and donating to the relatives, then one achieves two rewards at a time: keeping ties with kinship and charity. The evidence for this is that the Prophet said: "Donating for the poor is an act of charity, but donating for a relative is charity plus keeping ties with kinship." [Ahmad, An-Nasaa'ee, Ibn Maajah, Al-Haakim]
Allaah Knows best.