How to combine two string randomly in php

I want combine two words to get a list of other words containing its letters.

examples:

input: jack & sara

output: jaca, jara, jacka, jacra, jsara, jacara, jackra, jasara, jackara, jacsara

input: sara & jack

output: sack, sark, sarak, sarck, sjack, sajack, sarack, sarjack

I want to take the chars of the two words randomly to create those lists