Performing Hajj on behalf of the deceased

Q: Our family was afflicted by a drowning accident, the result of which was that my parents died along with three sisters and a brother. One of those sisters was only twenty-three years old, one was only twenty years old, and the third was only fourteen years old while the brother was nine years old.I have some questions related to the members of my family who passed away and I hope that you answer them. May Allah reward you with the best. My mother (may Allah be merciful with her) already performed Hajj (Pilgrimage). She wanted to perform it again but she died before doing so. On the other hand, my sisters (may Allah be merciful with them all) did not perform the obligatory Hajj.Q 1: What is the best thing to be done for my mother and sisters (may Allah be merciful with them all) regarding the issue of Hajj? (Part No. 9; Page No. 67) Is it permissible to hire some people to do Hajj on their behalf or should we do it ourselves on their behalf - bearing in mind that we want to choose the way that entails more reward?Q 2: My sister who died when she was twenty-three years old (may Allah be merciful with her) attained puberty when she was only thirteen years old. She did not observe Sawm (Fast) in Ramadan for two years. Afterwards we knew that she had to make up the missed Sawm and do the Kaffarah (expiation). She started the two months Sawm but she died before completing them even though she (may Allah be merciful with her) had intended to do Sawm for the full two months. Also, we do not know how many days she could not make up? What suffices her missed Sawm; observing Sawm on her behalf or giving Sadaqah (voluntary charity) as such?Q 3: My sister who was fourteen years old (may Allah be merciful with her) was born on the twenty-first of Dhul-Hijjah in the year 1396 A. H. And died on the sixteenth of Al-Muharram in the year 1410 A. H. Thus, she died one full month before turning fourteen years old. She attained puberty seven months before she died, meaning, she did not observe Sawm for six days of Ramadan. What should we do for her? Was Hajj obligatory on her? Do we have to observe Sawm for the six days of Ramadan that she did not make Sawm because she was pubertal at that time? If Hajj or Sawm should be made up on behalf of my sisters or my mother, who is the best person to undertake this amongst the relatives - bearing in mind that the rest of the family chose three brothers who are all pubertal, capable, and sane?Q 4: During this accident a bag containing some of my money sunk in the River Nile. Some of this money was a remnant of the Zakah (obligatory charity) that I intended to pay in Egypt. Should I (Part No. 9; Page No. 68) give Zakah instead of the sum of money that I lost?Q 5: Does my brother who drowned when he was only nine years old need any of our Du`a' (supplication), Sadaqah, Hajj, or `Umrah (lesser pilgrimage)? Thank you very much.