1 15" and 2 8 inchers in the boot....
AAAAARRRRRRGGHH.......don't do it, they'll cancel each other out, and apart from that, sound sh1t!
Get the biggest size you can up front (16 or 17cm) and power them with a decent 2ch amp, and then either a single 10" or single 12" in a sealed box (depending on what kind of music you listen too) powered by a mono amp, therefore sending a complete low frequency signal to the sub. Try not to read too much into the whole MAX WATTS figure as they are more than likely to be inaccurate of the amplifiers power. My Genesis profile 4 is only 4x75w RMS, but when bridged powers a set of Focals a treat.
With the set-up you've mentioned I would bung 3 of the 8" subs in a sealed box being run off of the big amp, and run the front set-up of mid-range and tweeters off of the smaller amp. I personally wouldn't bother with the other set of mid-range speakers as you can mess up the sound stage something rotten.
Lewy