MacBook – the maximum supported resolution of the MacBook Pro (Retina, 13-inch, Late 2013) for an external monitor at 60hz

I had this exact same question, and found the answer on Apple's discussion forums:

A final update - I got my hands on two Dell P2715Q's which support 3840x2160@60Hz over SST. I'm happy to report the new 13" RMBP happily drives both displays at their native resolutions with 60Hz refresh in single stream mode (the default).

https://discussions.apple.com/thread/6868583

You are outside "supported" territory with using three screens on that hardware.

• https://support.apple.com/en-us/HT204154 - thunderbolt FAQ
• https://support.apple.com/en-us/HT206587 4k and 5k and beyond

That being said, you can try connecting things and Apple hardware is known to run more displays than the "support" document allows. Usually it's due to driver updates that can still juggle all the connections but that the performance isn't there or you end up with glitches like frozen screens or just not the frame rates Apple likes to see on supported hardware combination.