You jumped right in and coded. See reply #29. If your coding is weak, then it's especially important that you have a definite, complete and bulletproof plan from the outset. That seems to me, missing.
There are things in your latest code that will "never fly", but I think it is premature to address since once you have a solid plan, a lot of it is liable to change anyway.
For example,
if(R2 == 1503.67)
This is unlikely to ever become true, you need to think about why (but as a side problem). Mainly, you need to put an adequate design scheme in place. The circuits you post are fine, it's just that by themselves, they can't do everything that you are asking because you haven't clearly defined how they will be used.
You can not design a working system by throwing eggs at the barn until one sticks.
You said, "if the unknown is supposed to be 1.5k ohm it reads 1.503k", well what precision do expect? Not even considering ADC error, that would be well within 1%. So it shows a lack of understanding of measurements which you will have to improve on if you want to complete this project.
Eschew code writing. Instead talk (in technical English) about what you have to do. Specifics not generalities. You began in reply #19, but you need to add more detail.