Praise be to Allaah.
If the situation is as described in the
question, and you were breastfed by her for five complete feedings or more
within the first two years of your life, then her children from the first
husband are your brothers through your father and mother through
breastfeeding, and her children from her second husband are your brothers
through your mother through breastfeeding only, because Allah said in Soorat
al-Nisa’, when mentioning the women who are haraam for marriage
(interpretation of the meaning): “Forbidden to you (for marriage) are:
your mothers, your daughters”; then He said after that: “your foster mothers who gave you suck, your foster milk suckling sisters” [al-Nisa’ 4:23]. And because the Prophet (blessings and peace of Allah be upon him) said: “What becomes mahram (forbidden for marriage) through breastfeeding is that which becomes mahram through blood ties.” Saheeh – agreed upon. End quote.