Get a well-rated softgel form without iffy ingredients like caramel coloring.
I think at this point, they should just go straight to liquid with an eyedropper, no gelatin capsule or anything in order to try and rule out as much as possible.
The problem with an exposed liquid is that will definitely lose its potency a lot quicker. A softgel keeps the active ingredient somewhat protected from oxidation. It also depends on the level of antioxidant present in the liquid. This matters in the tail end of the bottle.