Adopt boy w/o genealogy?

I have two daughters. Elder one is 7 years old. After first child, due to my ill health doctors told I cannot get conceived. So we planned to adopt a baby boy. So we were searching for an orphan. But in the meantime, fortunately with Allah’s grace, a miracle happened in my life. I gave birth to a girl baby one month ago. But my husband is willing to adopt a baby boy still. Actually we are planning to adopt a child from orphanage whose genealogy is not known to us. We do know that legal adoption is not permitted in Islam. Can we adopt a boy baby and upbring him along with us? If I breastfeed that adopted boy baby, will he become mahram to me and my daughters? What will be the relationship between us and that child? Will he be considered as our heir in future or will be just a sponsored child? If he is considered as sponsor child alone then is it permissible for us to permit him to live with us as one of our family member? Is this act permissible as per Shariah? Shall we proceed to adopt?