Re: 48w + 445nm handheld laser module
They want you to combine at least 3 lasers using only the cubes.
You can rotate polarization using waveplate, so combining 2 lasers using a PBS and overlapping beams is easy still.
What they are getting at is, after you combine using a cube, you now have a beam comprised of one beam polarized |, and the other beam polarized -, but superimposed.
The use of a PBS is exactly to split a beam that has | and - polarization elements into two beams based on their polarization. So, once you send that combined beam through another cube to add another beam, yes the beam will be added into the beam. At the same time, another beam with the same polarization that is already present from the first cube, will be split out of the beam.
Pony Beam Spitter may be a better way to approach this problem.