Can I get a warm upright piano sound live with two dynamic mics close to the strings?

Yes. Use two SM57s or Beta 56s placed inside the piano, 2–3 inches from the soundboard—one over the bass strings, one over the treble section. Angle them away from the hammers to capture the felt thud, not the slap. Close the lid to avoid harsh reflections, and pull the piano out from the wall a foot. In the mix, roll off around 7 kHz and add subtle compression. The warmth comes from proximity effect and the felt, not an expensive mic.