Droplets can be absorbed well through the skin in areas with little fat. I’ve never tried them, but if it’s stronger, you’ll want to use it less often
You want vitamin D to raise your 25(OH)D levels, and D3 has been shown to do this the best. Supplementing D2 is unnecessary as long as you have enough D3. I think the only way to acquire D2 is from mushrooms, whereas you get D3 from sunlight, oily fish, eggs and dairy.