Are ''kuliko'' and ''zaida ya'' interchangeable?
In this context no. Zaida ya would mean 'more than'.
But in the sense Emilian is tall, more than Esther?
You have it right, Cognocto. They both mean "more than".
So, what about kupita? It also means 'more than' How is it used?
Emiliam ni mrefu zaidi kuliko Esther.