WDYTO Tessa? I love it, but can't stand Teresa / Theresa.
What is a formal name that could give you the nn Tessa, other than Teresa/Theresa? Theodora / Teodora? I'm weird and think that Tess stands on its own better and you could maybe use Tessa as the nickname.
What MN would you give Tessa (slash the more formal name that gives you the nn Tessa)? Tessa Violet, Tessa Grace, Tessa Caroline, Tessa Liv, Theodora Noelle, Theodora Jane, Theodora Pearl, Theodora Nicole
Lilah and Tessa as sisters? Oooh, perfection! I love it!