No. Bob Martin used to kill cats. They've recently changed to using Fipronil as the main ingredient, which is the same as Frontline. If you use both you'll overdose them.
However fleas are becoming resistent to Fipronil, so neither will work very effectively. You really need either Advantage (which can be bought without prescription), Advocate, Stronghold or Broadline. But never use more than one at a time of anything.
I've just realised you mean one for one cat and one for the other? That's OK I suppose (as long as you have the Fipronil Bob Martin and not one containing permethrin - which is the dangerous stuff). You'd be better off with one of the other treatments I mentioned though.
You can read the ingredients on any product. If it contains permethrin then bin it.
I'm not sure what you mean about using something alongside something else. Do you mean using one thing on one cat and another thing on another? That shouldn't be a problem. Use any of the products I mentioned above, but don't use two products on the same cat at the same time.
And no, definitely no massaging! You part the fur to reveal a patch of skin at the back of the neck and dot the product onto the skin.