Doubt on Sookshmadarshini movie

How is grandma’s disappearance add value to their plan to kill Diana? If it was to bring Diana to India, they could have just lied to her and kidnapped her from airport as soon as she arrived rt? just like how they kidnapped her from airport later.

One more important plot hole is, when they already have a newly constructed bakery thats yet to be opened, they could have chose that place to kill Diana and burn in acid , as they were doing with her partner at the end of the movie . Why to even choose the house for that?