Hello,
I have a good background in developing HTML5 multi-player games. I can implement for the client and server part for this game. From the short description you've posted here I think the most challenging part will be to implement the server backend (the client with moving circles physics, splitting etc ... seems pretty straightforward). That being said, there is absolutely no benefit in using a beast like Unity for such a "simple" 2D client interface, plain JavaScript + some light JavaScript engine should be more than enough. I will test the client part in desktop and mobiles on all current modern browsers (Chrome, Firefox, IE11 and Edge, Safari, Safari Mobile iOS8, Chrome Mobile on Android 5).
We can discuss the details if you are interested to work with me.
Thanks,
Paul