Does that make Ravan the grandson of Tadka? Do the scriptures mention Sund and Sumali to be the same person?
As per Valmiki Ramayana, NO:
Tataka was daughter of a yaksha named Suketu. She was married to Jambha's son Sunda. Tataka and her son Mareecha attained demon-hood due to curse of sage Agastya. ~Valmiki Ramayana: Bala Kanda: Sarga 25
On other hand ...