Are the suckling brothers of my wife, from her father's other wives, considered mahram to my wife and her children, given that he suckled with her from her mother, and she likewise suckled from his mother during the suckling period?

Those whom you mentioned are considered unmarriageable (maharem) to your wife and her children. They are brothers and sisters to your wife, and maternal uncles and aunts to her children. This is due to Allah Almighty's saying: "Prohibited to you are your mothers, your daughters, your sisters, your paternal aunts, your maternal aunts, your brother's daughters, your sister's daughters, your foster-mothers who suckled you, your foster-sisters from the same suckling, your wives' mothers, and your stepdaughters under your guardianship, born of your wives to whom you have gone in. But if you have not gone in unto them, there is no sin upon you [to marry their daughters]. And [also prohibited are] the wives of your sons who are from your [own] loins, and that you take [in marriage] two sisters simultaneously, except for what has already occurred. Indeed, Allah is ever Forgiving and Merciful." (An-Nisa: 23). And due to the Prophet, peace and blessings be upon him, saying: "What is prohibited by lineage is prohibited by suckling." (Agreed upon). This includes those who were suckled by the mother and those who were not.