It may also be worth noting that people with excess body fat will absorb fat soluble vitamins into the excess fat and it will not be available for the thousands of functions in the body that need them until the person is fat adapted. Ideally the high priority goal should be to remove the excess fat but until they do they will need more than the RDI of each component. How much more gets complicated as there are not yet any good tests for testing how much was absorbed into the fat.
You would have to take a lot of vitamin D supplements to cause clinical symptoms. Some people have done it, but as a practical matter the risk of hypervitaminosis D from regular multivitamin pills is virtually zero.
Whether those pills actually have any health benefit is a separate issue.
Not always. Fat-soluable vitamins (A, D, E, and K) will build up in fat tissue and can lead to toxicity.