Praise be to Allah the Lord of the Worlds.

When a woman whose husband has sons from a second woman suckles a baby-girl then this girl becomes the foster-sister of this man`s sons from both women, because the Messenger of Allah Says (What means): "What is unlawful by reason of consanguinity is unlawful by reason of fosterage." {Related by Bukhari & Muslim}.

The husband who impregnated the suckling woman causing her to have a milk yield becomes the father of the suckled girl and his sons, from all his wives, become her brothers by virtue of this suckling. Jala aldin AlMahali (May Allah have mercy on him) says: "The suckling woman becomes the mother of the suckled child and her husband, who caused her to make milk through impregnation, becomes his/her father. Moreover, the marital prohibition on grounds of this fosterage applies to the man`s children; thus, they become the suckled child`s brothers and sisters." {Shareh Al-Minhaaj, vol.4/pp.65].

Al-Khatib Al-Shirbini says: "Marital prohibition due to fosterage passes from the suckling woman and her husband to their ascendants, descendants and brothers and from the suckled child to his/her descendants." {Moghni Al-Mohtaj, vol.5/pp.137}.

In conclusion, the children of the second wife mentioned in the above question, are considered your (Asker) maternal uncles by virtue of fosterage. And Allah The Almighty Knows Best.