Can you use products from different lines together?
Absolutely.
Although most brands will suggest that you buy an entire range of products from them, the fact of the matter is that many brands don’t offer all the solutions that a consumer might have.
Use your own judgment and don’t be scared to disagree with a salesperson at a counter trying to sell you a complete line. You might instead want to go into a place like Sephora or Shoppers Drug Mart, and find a knowledgeable sales person who can take you through the store and find you the treatments and products you need from a variety of lines.