I have used rnp over both CND Shellac and OPI and Gelish and removed it using a non-acetone polish remover. I also use either CND Shellac or OPI GelColor base and Gelish topcoat and find that they are durable but fairly easy to remove combinations. With all gel polishes, the key is allowing a thorough soak for a long time, keeping the pad saturated and firmly in contact with the nail. Adding a little heat also helps.
CND Shellac is a hybrid product, that is, it contains solvents and hardens both because of the evaporation of solvents and the polymerization under UV light. That applies to its base, color, and top coats. With OPI Gelcolor, only the base coat is hybrid; Gelish is not hybrid and its top coat is acetone resistant. Of course, application, how long its been on matter, but all else being equal, when it comes to removals, Shellac tends to be the easiest, then OPI and then Gelish. All of them are removed using acetone based removers. Just because something is acetone free doesn't mean it is gentle. Some of the solvents in acetone-free removers are pretty powerful, even toxic. Try different brands with different solvents. So to remove rnp over gel, saturate the pad with the remover, put it on the nail for only a few seconds and wipe. Don't let it sit on the nail very long. Better to apply and wipe a couple of times than to let it sit.