Loose Seat/Seat Belt problem 94 K Blazer

[mrsmoos]

We are looking at buying a 94 full size Blazer for our son's first car. The thing is pretty good except for the passenger side front seat seems loose --kinda "rocks" and doesn't seem like it would be safe. Is this "fixable" or replaceable?
Also, both front seat belts don't "snug up". You put them on and then try to pull on them to "snug" it across your chest but all they do is get looser. I saw some replacements in a catalog but are they hard to replace and make sure they are SAFE? Any advice would be appreciated.
Thanks
Worried Mom