You need to look at, or at least consider, the existing plumbing that comes before the shower valve - the size of the tubing, the number or fittings, etc.

If the supply tubing is 1/2", then you may not be able to take advantage of all of the flow-through that a 3/4" shower valve would provide had it been plumbed with 3/4" supply tubing on the shower's branch lines.

That said...yes, 1/2" supply tubing can supply enough water to feed two shower heads. Shower heads are limited to a max flow of 2.5GPM, and half-inch supply tubing that doesn't have any wacky restrictions (too long of a run, too many twists and turns in the run, flow restictions due to sediment/corrosion, decent water pressure, etc) can feed 5GPM.

As to your valve being able to supply sufficient flow through to the two heads, that should not be an issue. Just check the valve's pass-through, it should be above 5GPM.

If you do have flow restrictions, you could help performance by using a shower head with less flow through.

Thanks Mongoct!