I think you could train them twice a week with benefit but that depends upon how hard you are training them. Consider that you are not only working them on an arm day but your chest and back day work them pretty darn hard as well. Maybe share with the group what you have in mind for the arm work.
The shoulder movements you have chosen are all pretty good. I like standing rows, face pulls, barbell and dumbell shrugs, and bent over shrugs as well.
Cable work can be very productive as well. If you have access to a duel cable high / low pulley then consider some laterals and rear delt flys using the cables.
I also make myself do a short static hold at the peak of most all of these movements. Just a second or two will make a big difference to the effectiveness. Rich Gaspari wrote about this years ago and I incorporated the squeeze into everything from bicep curls to barbell rows. It makes a big difference.
One thing that my old coach taught me about pressing movements is that just because your arms are extended does not mean you are done lifting. And he is right. I can generally squeeze a bit more ROM by contracting my chest or shoulders at the peak once my arms are extended and get an inch or more to the ROM. This tends to really squeeze the chest or shoulder muscles and makes the lift more challenging and productive.
Maybe some of this will help you. Good luck.