1) on your brother demise his second wife , 2 daughters and mother are the legal heirs
2) each have 1/4th share in his property
3) for sale of trucks you need your bhabhi signature too
4) you cannot operate trucks without consent of all legal heirs
5) for transfer in name of elder daughter consent of other legal heirs are necessary
6) apply for succession certificate in district court . enclose copy of death certificate and other documents
7) contact a local lawyer