Need a pipe change when install a double basin vanity?

[ELLGGG]

I am going to replace the old single-basin vanity with a new double-basin vanity in my bathroom. Now I have two mixing taps but there is only one hot and one cold water inlet on the wall.

Can I just use a 15x15x15mm Tee on the hot or cold water inlets on the wall to split water supply to two mixing taps on each basin? or I have to change the old 3/8" pipe with a new 1/2" pipe from the main pipe to the wall inlet first and then use a 20x15x15 Tee to split the water supply to two taps.

Hope you can understand what I am asking.

Thanks.