In Seed of Chucky (2004) how is Glen able to bring Tiffany's and Chucky's souls back into the new dolls? It's as though he just kinda plucks them out of nowhere. Reciting the incantation like this could've brought just about anyone into those dolls.
At this point in the franchise, Chucky and Tiffany are long since dead (Bride of Chucky, 1998). The dolls Glen finds are movie props, created from the legend of the killer dolls.
In every other soul swapping occurrence (attempt) in the franchise there has been at least two bodies involved. Charles Lee Ray and The Good Guy Doll, Chucky and Andy, Chucky and Tyler, Tiffany (even though she's already dead in the bathtub) and The Bride, Tiffany and Jennifer Tilly, Glen/Glenda and the babies.
Glen just walks up, says the chant, and Tiffany and Chucky's souls are back.