He found a baby and adopted him – what is the ruling?

Dear Brothers & Sisters,
As-Salaamu-Alaikum wa Rahmatullahi wa Barakatuh. (May Allah's Peace, Mercy and Blessings be upon all of you)
One of our brothers/sisters has asked this question:
My father found a baby at the top of a mountain and saved his life. My mother looked after him and her breasts started producing milk without her having a child of her own, so she breastfed him for two years. The child grew up and was brought up with us, and my father gave him his name. My father and mother have both died, and my father left instructions in his will that this boy should inherit along with us. Is it permissible for him to inherit along with us, and what is the ruling on his relationship with the women of our family?.
(There may be some grammatical and spelling errors in the above statement. The forum does not change anything from questions, comments and statements received from our readers for circulation in confidentiality.)
Check below answers in case you are looking for other related questions:
It is not permissible to name the orphan after your husband for the purpose of sponsoring him
If a child is the illegitimate offspring of two kaafirs, can he be named after the zaani?

Answer:
Praise be to Allaah.

Firstly: 

Your father and mother are to be thanked for what they did, taking care of this foundling until he grew up. 

Secondly: 

Radaa’ah or the breastfeeding that makes the child a mahram means giving five or more feedings within the first two years of the child’s life. If your mother breastfed this child in this manner, then he becomes a son for her and her husband through breastfeeding, and he becomes a brother to all their children through breastfeeding. Allaah says (interpretation of the meaning): 

“Forbidden to you (for marriage) are: your mothers, your daughters… your foster milk suckling sisters”

[al-Nisa’ 4:23] 

“The mothers shall give suck to their children for two whole years, (that is) for those (parents) who desire to complete the term of suckling”

[al-Baqarah 2:233]

And it was proven that the Prophet (peace and blessings of Allaah be upon him) said: “Relations through radaa’ah (breastfeeding) makes all those things unlawful which are unlawful through corresponding birth (blood) relations (i.e., prohibited marriages).” Narrated by Maalik, 2/601; a similar version was narrated by al-Bukhaari, 3/149; Muslim, 2/1086. And it was narrated that ‘Aa’ishah (may Allaah be pleased with her) said: “One of the things that was revealed in the Qur’aan was that ten recognized breastfeedings makes all those things unlawful which are unlawful through corresponding birth (blood) relations, then that was abrogated and replaced with a verse that mentioned five, and the Messenger of Allaah (peace and blessings of Allaah be upon him) passed away when that was the ruling.” Narrated by Maalik, 2/608; Muslim, 2/1075 

It should be noted that what is considered to be one breastfeeding is when the child takes hold of the nipple and sucks milk from it; if he lets go, then comes back and sucks more milk, this is a second breastfeeding, and so on. 

Thirdly: 

It is not permissible for the child mentioned to take your father’s name as if he is one of his sons. 

Fourthly: 

The child mentioned cannot inherit from your father, because he is not one of his heirs. 

Fifthly: 

If it is proven that your father left one-third or less of his estate to the child mentioned, there is nothing wrong with that; you may also keep in touch with him and treat him kindly, for Allaah will never cause the reward of those who do good to be lost. 

And Allaah is the Source of strength. 

Whatever written of Truth and benefit is only due to Allah's Assistance and Guidance, and whatever of error is of me. Allah Alone Knows Best and He is the Only Source of Strength.
Your brother and well wisher in Islam

Related Answers:
She wants to raise an illegitimate child with her sons
He adopted a little girl, and her parents are telling him to give her back, but he fears she may be misguided if he gives her back. What should he do?
A family adopted him because his family were bad people, and they gave him their name; what are the consequences of that?
It is not permissible to name the orphan after your husband for the purpose of sponsoring him
If a child is the illegitimate offspring of two kaafirs, can he be named after the zaani?

Recommended answers for you:
He has a number of questions about zakat al-fitr
Fatwa from the Standing Committee on the “Business and “Hibbat al-Jazeerah” companies and pyramid marketing schemes
Rulings to do with abortion
Is it recommended to fast ten days of Dhu’l-Hijjah including the day of Eid?
Circumcision: how it is done and the rulings on it