Road tires (700c) will NOT work on 26" mtb rims, end of story.
And road rims won't fit in a mtb frame, at least not very well or safely.
3rd the recommendation of getting slicks 1.25-1.5" or so.
Depending on your intended usage, you can get something like the Ritchey Tom Slicks, or if you ever wanna ride on moderate to easy trails, you could get some Ritchey Cross Max tires (they are harder to find these days, but I got some cheap online someplace, I wanna say for like $15 a pop) which have an inverted tread, so they roll decently on roads, yet are still somewhat useable on trails.
I did just this many moons ago on my old Rockhopper mtb, and then also got a 48t big ring for it, so I got less spun out at higher speeds, and it works reasonably well. www.qbike.com
is a good site to shop price online, and of course if ya find a particular tire ya like, Google is your friend as well.