Between Vinda Rosier from Crimes of Grindelwald and Felix from Hogwarts Mystery, the new material in the Wizarding world is making me think we need an official Rosier family tree. But, for lack of an official one, I’m going to do my best to work it out.
Let’s start with the youngest known family member and work backwards. Felix Rosier is about 2 years older than Bill Weasley, meaning he was born in 1968 or 69. If this bit of dialogue in Hogwarts Mystery is to be believed, his father was “a top Death Eater”.
The past tense makes me think they meant for Evan Rosier, who is dead by this point, to be his father, but that doesn’t actually work. Evan Rosier was one of Snape’s peers, and Snape was born in 1960, giving them an age difference of only 8 or 9 years. They could be brothers or cousins, but not father and son. For simplicity’s sake, let’s assume they’re brothers and that the past tense is because Voldemort is no longer around. (Alternatively, both died during the war).
There are a few other notable members of the family. One is Druella Rosier, who married Cygnus Black. Another was one of Tom Riddle’s school peers who went on to become one of Voldemort’s first followers. To be near Tom Riddle’s age, he would have had to be born in the late 1920’s, around the time of the first Fantastic Beasts movie. I think it makes a lot of sense for the new character of Vinda Rosier in Crimes of Grindelwald to be his mother, although she could also be an aunt. Druella’s age is not given, but her husband was born in 1938; if she is near his age, she could be either a much younger sister or a cousin to the Rosier who was at school with Tom Riddle.
That character could easily be Evan and Felix’s father. He would have been in his mid-30’s when Evan was born and in his early 40’s when Felix was born if that’s the case. He could also be Felix’s grandfather if both he and his son had children in their early 20’s, although in that case Felix and Evan would probably be cousins, rather than brothers. And, of course, it’s also possible that he’s the father of one and the uncle of the other.
Or, in other words …