Is it okay to use Stieva-A and Ultraquin at the same time? And do I just put one on top of the other and then a moisturizer?

Both Stieva-A (tretinoin or another brand of Retin-A) and Ultraquin (hydroquinone) should be used only under the care of an expert in skin rejuvenation. Both are used on top of basic skin care. This is a good cleanser, an alpha or beta hydroxyl (both can be in the same bottle), a pH balancer usually with an antioxidant and a good UVA sunblock. Notice that there is no moisturizer as it is the WORST thing you can do to your skin. It stops the skin from moisturizing itself, breaks down the skin cell's walls and weights down the skin encouraging more wrinkles. The 2 you mention are then added to treat wrinkles and spots. (See PlasticSurgeryToday.com/beautifulskinlaserresurfacinghighlandsnorthcarolina/obagi-nu-derm/)