I have INQ Medival Town tile set and I am wondering if I use that tile set for towns and the original rtp for forests and what not would that be bad? - like would it severally clash?

Go for it.

[Spriters will tell you] The truth is having tilesets sync is far more difficult than most people suspect. Experienced artists understand there is a deep chemistry behind the color palettes and pixel count. Unless you're going for a very professional quality, I would say those tilesets should work together. There is a limited supply of large resources online (that are already cut, arranged and ready to import), so just go for what you like.

My only advice in the future is avoiding going from very bright tiles, to very dark tiles. For example, Secret of Mana tree's wouldn't suit a Final Fantasy VI town. Those are usually the worst examples of bad tile-symmetry I find. Or using tiles which are way too big for the sprites.

I have all of his tile sets but indoors looks like something out of Willow (Snes game) and so does out side, I am going for FF looking game - with out actually using the tile sets...

I'd say why not...Ive done it myself countless times, and never regretted it. There are so many edited
RTP versions, meaning people are still choosing them over other alternatives. But no, I don't see any
clash between the two tilesets.

Um, I dunno - I mean the original tile set (but i have a master version that has most of the out doors compiled into one major tile set) that comes with the rpg maker and inquisitors our door version...

Are you sure this wouldn't clash?

It comes down to how you use them. INQ's tilesets are incredible, and you should give them a go.
However, using them with the RTP house interiors etc is a no go area. The Cave sets and Mountain
sets for example seem to work fine. Infact, using INQ's 3 tilesets, thats all you really need.

I was more woried about out doors, indoors will be his, world map will be his.

@ Adrien. Like I said, don't be afraid to use RTP like cave sets etc with INQ's.
Infact, thinking about it, there are even other tilesets that match the same palette as INQ's.
For cave sets, I can pm you one.