Wills, identity certificates and death certificates of brother-in-law and two sisters (issued by the police station), family relationship certificates of brother-in-law and two sisters, relationship certificates of you and their relatives (issued by the neighborhood committee), certificates of no other legal heirs, and house title certificate.
2. Who needs to attend?
Testamentary succession usually requires the presence of legal heirs. Judging from your situation, your sister has no other legal heir, and the only legal heir of the untreated part of the estate is you, and no one else is needed.
The second question: The real estate license is my brother-in-law's name. After my sister-in-law died, my sister didn't go through the formalities of changing her household name in time. Will it be a problem for me to handle the inheritance procedures and transfer the property now?
In this case, you need to prove the marriage relationship between your brother-in-law and your sister, and the time of their death.
The third question: Does going through the testamentary succession procedure for elder sister mean transferring the house to my name? If yes, I would like to ask: because I am old, if I want to register the name of the house as the name of my son and the son of my other deceased second sister, is it ok? If yes, what procedures are needed and which departments to go to?
Generally speaking, it is relatively simple to register in your own name first, and there is no need to pay taxes on the transfer of houses between relatives. Let's just say that from the perspective of inheritance law, because your second sister died before your sister, your second sister's son has no right to inherit your sister's property.