I don't know what UP/UC means. Does that mean that you are having no medical-type interventions or assistance?
Anyway...my impression is that 2 heartbeats at 30 weeks should be VERY distinct, even with a stethascope. I suppose if the kids were right on top of each other, maybe not--but it doesn't fall into my realm of experience, since my guys liked to be oppose diagonals from each other. (Can we say OUCH?)
I actually felt more movement with my daughter than with my guys. She was kicking, rolling, punching multiple areas all at once constantly. Generally, my guys would not get too active unless they were being monitored, when they'd both work to knock off the monitoring devices. My boys were relatively big though, and due to the TTTS one of them had limited mobility. I felt more "internal" movements (not kicks or punches at me--they primarily liked to wrestle with each other). Kind of like how when your kiddo has hiccups it's internal (since it's not something they're doing TO you, though you can feel it because its inside you). Except for this involved a lot of wrestling, twisting, and roiling.
Please allow me to be a worrywart former TTTS-survivor parent here, but if you really think you are having twins, it might be a good idea to talk to someone (CNW, doc, experienced midwife, ect.) who can confirm whether or not you're having twins. If not, then you don't need to worry about it. If you are, then that way at least you have someone who can advise you if you start experiencing some problems (though chances are you won't, you'll just need to make sure you've got double supplies of birthing stuff ;>)