Translation:I am calling them
It is not a question of being plural or not: the -eni suffix is there to solve the ambiguity between 'you (pl)' and 'them', since both use the object infix -wa-. There are actually three ways to solve this issue: E.g. for 'I am calling you (pl)':
Add ninyi to remove the ambiguity: Ninawaita ninyi
Ninawaiteni: this is what DL teaches us, and apparently the most common construction.
Ninakuiteni: using the singuar -ku- infix for you, but using the plural -eni suffix.