What do i do? My mom ped away suddenly and handling her affairs + siblings. support? advice?

My mother ped away recently and i am her oldest son. I have 4 siblings. i have lived out on my own since 17. Dropped out of school to help pay bills when mom was laid off. need to support my family. even with 4 months of school left. ive done many adjustments to my life and have a steady job now. With the recent events happening has thrown me through a loop. I am executor to her estate but i am 20 years old and am completely oblivious to what i need to do. her fiance of a couple years has a business in her name and he wants the house they bought together as well. which is also in her name. she also has a vehicle which she's paid half of. i want that. i need a vehicle and have all means to keep it. but with no credit or credit history, nothing, i cant get financed. i have no option to get a credit card to build credit, cant do anything without a co-signer which is almost impossible for me. i dont have anyone. meanwhile my sister who has two kids, and i do not like her whatsoever, love yes. only because its my sister. my two neices are precious and i do not take it out on them and my mom had two houses in her name. one of them has a mortgage and owed a lot of money still. but my sister wants to rent it. she lives on the system and is a bum. but my neices deserve a nice home. i would be willing to rent to her if the mortgage gets paid and i will make checks to make sure its kept in clean function. my 2 brothers moved over an hour away and i never see them but they are with my dad who i feel is the best possible place for them to be. my younger sister just had a baby at a young age and she was probably the closest to my mom a believe, if there is such a thing as who's closer. anyways she stays out and works with my moms fiance at the business he manages. i have expressed to her multiple times she does not need to feel trapped or theres nowhere else to turn. she doesnt have to change her opinion because he thinks its right. not that he is influencing her that way but if a time arises where shes had enough. anyways. so i do not know what this feeling is i have. i think it may be overwhelmed? so i dont believe ill be able to keep the car. i live with my best friend. have since i left home. and i dont need the houses but i could use them for my family who does need. hospital bills and debts add up though as well. funeral cost was the only thing i could take care of with her bank accounts. maybe i need more organization or some really good guidance. can anyone relate, or know what i could do to make my life a little easier..