should i replace the tires/tubes to sell vintage bicycle?

If it's really vintage (collectible) and has value for being vintage and the tires are original, don't change them.

When people buy vintage (collectible) thing, they want everything vintage, even if not immediately usable; if you change anything thing, it will loose value (as a collectible object)

The best thing would be for you to find good working order original tires.

Usually when we're talking about bikes from 15+ years, you most likely won't get the money back which you put into it. Also many people buying vintage bikes are either collectors or hobbyists who prefer all original as Max pointed out, or they'll want to restore the bike and pick the tires themselves (picking parts for projects is part of the fun).

I would sell it as is, just clean it up and take good pics (the first pic should always be side-on from the drivetrain side).