Sister in-Law to Nurse my Son without my Husband's Consent

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My question was regarding whether I can have my sister in law nurse my 15 month old son so he would become her and her daughter’s mahram. The complication is that my husband finds this idea really strange and for no valid reason is saying no. I have a very good reason i want to do this which is that once he is older, I want to be able to easily let him visit my brother’s house and not have them to worry about him not being their mahram. We go there a lot because our kids play and I don’t like to be at the unislamic environment of my in-laws house. I don’t want to have my son go to my husband’s family’s house too much because they listen to music, have m..........click on the link above