You'll want to verify the sizes are correct - easiest way to do that is to just pop the shower head off your wall and bring the whole thing to your local hardware store and see which parts are a fit, but, starting at the wall tap:

1/2 in. Brass PEX-B Barb x 1/2 in. FNPT Adapter | $3.43 (x1) Connect this to the wall tap, then attach a section of tubing to it, set in place with a hose clamp.

1/2 - 1-1/4 in. Stainless Steel Hose Clamp (10-Pack) | $17.98 (x1 bag of 10) You can buy them individually too, but a few extra never hurts - these things are super handy. You might want to additionally hit these with a zip tie, which will compress the excess metal back down against the hose: when its fully tightened, there will be a tab that sticks out, which can cut you if you snag on it, especially when your skin is soggy from the shower.

3/4 in O.D. x 1/2 in. I.D. x 10 ft. PVC Braided Vinyl Tube | $17.97 (x1) 10 feet should be just enough - measure carefully before cutting. Also the braided reinforcement is mission-critical: non-reinforced vinyl tubing will get soft with the heat, then balloon and eventually burst.

1/2 in. PEX Crimp x 3/8 in. O.D. Compression x 3/8 in. O.D. Compression Quarter Turn Dual Shut-Off Stop Valve | $22.97 (x1) ...I've seen better versions of this - you want a barbed connection on all three ports, not the hex nuts like this one has... but those should still do the trick if you discard the nuts and clamp the hose down on the threads. Might need some locktite or something to really seal it down, since spiral threading could give the water a path out.

Power Lock Suction 6 Robe Hook Combo Pack in Clear | $10.92 (x1 needed, but an extra set can help manage the tubes) Mine are a little different, but you want suction cups that have a dual action mechanism like the ones linked. Regular slap on suction cups will fall all the time. These ones will still fall, but maybe like once every couple months. The ones I have are a twist-to-seal mechanism, but I don't see that model now - but these ones have only failed a couple of times, like once every 6 months. Clean the application site thoroughly so it's got as nonporous a surface as possible.

From there you'll need a total of two shower heads and two suction shower mounts. The price of both varies a ton, but I'll leave model selection to you since there are a lot a features you may or may not care about. You can save a bit of cash if you use the one already installed in your shower, but we forked out a bit of extra cash to get a matching set. Don't forget to remove the pressure regulators from each one, or you won't have good pressure from either head.