Legally adopted child versus brothers and sisters of the deceased

Dear PAO

My eldest sister died due to Covid-19. Her husband predeceased her. She was survived by their legally adopted child. From the beginning, we are very adamant accepting their legally adopted child in our family because we did not like her attitude. She is very nice to our sister and my sister's husband, but she never respected us. We always view her as "sipsip" just because my sister is rich. Now that my sister is gone and she left no will, their legally adopted child is claiming her whole estate. My siblings and I wanted to fight for our right, if any, on my sister's estate.