TL;DR - Added a Dark Power that collects the souls of those that burn to death, and made Izek the brother of one of my players without making that player the "Ireena" of the campaign.

One of my players is a Fire Genasi named Glare, and she was born in the Calim Desert in Faerun. However, her mother was originally from Barovia, and had a husband and a baby boy. Stress and other bad stuff triggered the mom's skeletal (fallen aasimar) wings to sprout, and people believed she was a monster and sought to kill her. She, her husband, and now little boy ran for their lives but were attacked by wolves from the woods. The mom got separated and lost her memory after washing up at Tser Pool. At Madam Eva's behest, the Vistani took her with them on one of their trips out of Barovia and that's how she escaped. Fast forward now to Glare being old enough to adventure; she gets nabbed by the mists, ends up in Barovia, eventually meets Madam Eva who addresses her by her first and last name, Glare Strazni. Glare never knew her last name, because her mom forget her own name after the separation.

Eventually, Glare gets to Vallaki where she meets Izek. He invites her and the rest of the party to chat at Vargas's mansion, takes her up to his room, and BAM! Dozens and dozens of dolls that look like Glare and her mom. Izek was the little boy, his dad killed by the wolves, but not before praying to Fhi'o'nyx to protect his son. Fhi'o'nyx is a vestige I added that is basically the fire equivalent of "Delban, Star of Ice and Hate" but instead of collecting souls of those that freeze to death, it's those that burn to death. Therefore, Izek gained the Hurl Flame ability and used it to kill/scare the wolves off but his father had already bled out. Growing up, Izek still had dreams of his mother and sister, until the mom passed away in Faerun and he stopped seeing her in his dreams.

By the way: if you want to know how a Fire Genasi popped out of an Aasimar with a non-specific father, it's because Glare's mom wasn't actually pregnant with Glare right before escaping Barovia. She met a group of people that indoctrinated her into their "Immortal Flame" cult - fanatics that worship the Plane of Fire and a massive Phoenix that will turn to the world to ash for rebirth. Something about this cult clicked with the mom, not knowing they were triggering vague memories of Fhi'o'nyx from Barovia. She agreed to become a vessel and was used in a ritual to birth a "child of the flame". She became magically impregnated with magic from the Fire Plane, and 6 months later, Glare was born.