dafiryde... I'm not you, so what I would do isn't necessarily what you should do. But, having said that, now that you own those two great, high-quality lenses, I would keep them. If you're interested in photgraphy enough to own a DSLR, chances are you'll want those lenses at some point in the future. Plus, you're likely to lose money when you sell them or trade them in.
That isn't to say you shouldn't get the 18-250. But since it costs something like half to two-thirdsthe price ofeach of the other lenses, I'd just add the 18-250 to my kit. If you don't have the money right now, it shouldn't take long to save up $400.