on the sims 2 for pc does it harm the game to move them from town to town?

It shouldn't harm the game, no. I've moved families from Pleasantview to Riverblossom Hills before. Maybe your game has some sort of glitch, like mine. :\

If the family was completely brand new and knew nobody outside of their family (nobody that lived outside of the lot) then you might be safe. But if they knew other sims, any other sims, you've created duplicates of those sim files in the neighborhood you've moved them into. How serious this is depends on how many sims they know - if it's just a handful you may able to continue playing without too much issue. But if you've moved a family that knows a lot of sims, or an old Legacy family, you've likely corrupted the neighborhood you've moved them into, creating tons of extra sim files. This is Very Bad for your game.

The only thing you can do at that point is delete the neighborhood you moved them into and start it over.

how the hell did you do that, please tell