Will yeast activate with equal

First off, it's good to understand the difference between active dry yeast and rapid rise yeast. Active dry yeast is a larger granule of yeast in which the outer shell is composed of mostly dead cells entombing the dormant nougaty goodness inside. It has to be proofed to seperate out all the cells and rehydrate the interior active cells.

Rapid rise yeast is a typically a combination of 2 different strains of yeast (so those with a very discerning palate might be able to tell the difference, I've never really tried). The granules of yeast are smaller and dried slower to preserve more yeast cells. Ascorbic acid is also added to push the yeast into overdrive a little faster.

A great video that helped me a lot is http://how2heroes.com/videos/dessert-and-baked-goods/yeast-101 I have noticed before issues with Rapid Rise yeast not proofing very well the second time around. Apparently it's designed to give you one really good proof and then die out (play hard and die young). Instant yeast however is Rapid Rise yeast without the hardcore party attitude. It's what they use at the King Arthur bakery test kitchen, so that's good enough for me! They say to use them interchangeably, but many other sites I see show a difference of about 20%.

2 Tbsp Active Dry yeast ≈ 1.6 Tbsp Instant Yeast

The existing answers already explain why yeast and baking powder won't work together. But even if they did, you wouldn't have a reason to use them.

You seem to think that fluffiness depends on the amount of gas produced by the leaveners. In fact, it depends on both the gas and the ability of the dough to trap that gas. If you produce too much gas (no matter whether through yeast or through baking powder), then the fluffiness will be less than when using the optimal amount of leavener. This happens because your dough cannot hold the gas and the bubbles break, resulting in the dough deflating like a punctured tire. So even if combining two leaveners would have resulted in more "blowing big" action (which it doesn't, see the other answers), you would not end up with a fluffier end product. If you want fluffy muffins, you have to use a recipe and a technique which is best capable of retaining the gas produced by the baking powder. The amount of gas production is not a bottleneck.