Giving away equity to new member in a startup?

I've been working on a startup for more than a year now, and as a developer, I created a nice product. But things got harder when I tried to sale it, as I have no talent for this. Then I met two people that would be really interested to do the sale job in exchange of equities.
I want to go further in this deal, and gave them 33% of equity each, so at the end of the process the company would be split equally. But, I don't want to give equities in exchange of nothing, so I want to give them max 5% each every 4 months if they reach financial objectives.
Here are a few questions

1. Does it seems to be the right way of doing this?
2. What should happen if they don't reach the objectives?
3. Are there other things I should add to the deal?

This is called vesting, and is absolutely the right way to go about it. There should also be a cliff, a minimum amount of time they need to work (usually 1 year) in order to actually get the equity they've been earning per month.

This is a good guide to creating equity structures: http://thestartuptoolkit.com/blog/2013/02/equity-basics-vesting-cliffs-acceleration-and-exits/