Cant get one of Karlach+Gale's endings

Im currently playing Karlach and I wanted to do the ending where he Karlach in the ending, turning her into a Goddess by his side. I got to romance Gale till the end (got all his romance scenes).

The problem is, if I become Illithid he does make me a goddess by his side, but I wanted full well Karlach there. But if I dont transform her, then he decides to go to Avernus with me and dont end up reforging the Crown.

Anuone knows if I need something else to make it happen?