First of all, your father has five brothers and sisters, and each should get 20% of the inheritance, not 25%.
Secondly, the name on the real estate license is the key. If your father's name is on the property ownership certificate, then the house belongs to your father and is not included in the inheritance (if you find out the evidence that your father contributed to grandma's house purchase, you can also). If the name on the property ownership certificate is your grandmother's, and your father can't produce evidence to prove that the house was purchased by him, then the house should be divided into five parts as an inheritance and distributed equally.
Thirdly, your sister-in-law has priority in inheritance (unless she gives up), but as compensation, she must give 80% of the house price to other brothers and sisters.
Finally, this is a typical division of inheritance. I hope your family can handle it properly, and I wish you a happy family and a happy New Year.