Can the Macbook Pro drive two Ultra HD monitors at 60FPS each?
According to this document https://support.apple.com/en-us/HT204154 The MacBook Pro (15-inch and 17-inch, Early 2011) and later have Thunderbolt2 and can handle two thunderbolt displays (2560x1440).

According to this document https://support.apple.com/en-us/HT202856 The MacBook Pro (Retina, 15-inch, Late 2013 and later) can handle one MST 4K display at 60Hz.

You can run one 4K monitor off of the Thunderbolt display at 60z and a second off HDMI at 30Hz. the two thunderbolt ports are connected. Once you try to connect a second 4K monitor to the other port, you will go over the bandwidth and the second monitor will go dark.