Her digital piano she has only had for 6 months is screwing up and her amp is not working. I have had to fix my new MacBook Pro already and it only worked for a few months after it was fixed and the wife's Mac book pro needs fixing too! I can see the salt in the air at night on my outside cameras.
I have some guitars, including parlor acoustic guitar made in the 1920's and some 50's-70's vintage electric guitars, so I understand your concern about musical instruments, BUT what the hell happened to your DIGITAL piano? I have Yamaha Clavinova, there are no parts that can be f@cked up by humidity. The same with MacBook Pro, I have two, the first one had some corrosion spots on aluminum surfaces, but nothing serious... The same with amps, I have tube Laney and Marshall, no problem at all in this climate (and I lived 6 years VERY close to the sea in Santo Domingo, and it's MORE humidity here than on the North Coast).
Maybe the answer is that I always use A/C, so the air is dry inside the apartment.... but in this case your problem is not the location. Or move to Jarabacoa, if you love to have your windows always open
P.S. there are NO safe areas in Santo Domingo. Welcome!