Take it literally. If it's an easy stage, then it's easy. I have Thoth and Tsovinar but only Tsovinar is the one I setup to be a Lead. But honestly any unit that has decent Leader skill will do for an Easy stage of The Savage Lion.

Ask me if you'd want a Tsovinar for F and read below to rethink if you'd really need either of the 3 you mentioned.

I just spammed Sasha UBB throughout and used 1 Osiris DBB (Magma) in phase 3 to beat this easy (which both were really unnecessary since this is an easy stage). Anyways, this should serve as proof you don't need Thoth, Aoife, Tsovinar, or Maeri in the easy stage of The Savage Lion. I only used Maeri as my F randomly and I didn't use her UBB. Any unit with decent Leader skill will do.

Thoth, Aoife, Tsovinar, and Maeri will matter so much in the Hard version of The Savage Lion.