I am from lahore pakistan my question is can i marry my sali ( wife younger sister ) My wife died few months back i have 2 small kids i am 40 year old my family and my inlaws family want me to marry my sali ( wifes younger sister ) when i got married my sali was only 10 year old i always treat her like my child now she is 20 my family says we should marry for the sake of my little childrens
You can marry your sister-in-law after your wife's death, because the prohibition is only in having marriage with two sisters simultaneously.
حُرِّمَتْ عَلَيْكُمْ ... وَأَن تَجْمَعُوا بَيْنَ الْأُخْتَيْنِ
Prohibited to you [for marriage] are ... that you take [in marriage] two sisters simultaneously
This is different from your wive's mother and daughters who are perpetually forbidden once the marriage is consummated, as expressed in the same verse.
حُرِّمَتْ عَلَيْكُمْ ... وَأُمَّهَاتُ نِسَائِكُمْ وَرَبَائِبُكُمُ اللَّاتِي فِي حُجُورِكُم مِّن نِّسَائِكُمُ اللَّاتِي دَخَلْتُم بِهِنَّ
Prohibited to you [for marriage] are ... your wives' mothers, and your step-daughters under your guardianship [born] of your wives unto whom you have gone in.
Also relevant : Who are the women that a man is forbidden to marry?
Just go for it your sali is good after death of ur wife no matter how young she is. You are lucky person to have such great opportunity with the permission of parents just marry her brother and make her happy on first night.