I haven't played my guitar in about a few years, I've kept it in the same place for a long time in room temperature. I cant really tell if the strings are rusted or not. But four out of six strings are sounding alike, no matter how I tune them. The two lower strings sound alike to one another. And the two middle strings sound alike to one another as well. Is this fixable or does this mean I need new strings?
Even well worn strings should be capable of being tuned. A quick rust check is to run a finger under the top two strings. If rusty, they'll feel rough. It's difficult to tell with wound strings, though.
A new set of strings will bring any guitar back to life, so it's worth the small amount to buy them. Lots of players change them each gig, each week, or at worst every six months, depending to a degree on how much they play, how acidic their sweat is, etc.
Put on a new set, and hear the difference!
What do you mean by “sounding alike”? A set of strings should sound “alike” in the sense of, the timbre should be mostly consistent across the range. More precisely, e.g. the F on the A-string 8th fret should sound very similar to the D-string 3rd fret: same pitch and just a little bit mellower timbre.
If you actually mean that the empty strings sound all the same pitch, and turning the tuners doesn't change that, then something is extremely wrong. Never mind strings, bring the guitar immediately to a luthier if that is the situation.
I change the strings on my guitar quite frequently due to tone loss. The best suggestion I've ever seen for strings is: when in doubt simply replace them. There is no reason to sacrifice good sound over a few dollars and people will like your playing more.