It's all about the impedance of the speakers, what impedance per channel the amp is capable of, and how you wire it. It's possible, but you need to make absolutely sure that you buy equipment that will match up and work together. For instance, two 4 ohm speakers wired in parallel on the same channel of amplification would make a 2 ohm load on that channel. The same four ohm speakers wired in series on that channel would create an 8 ohm load. Most four channel amps will be capable down to a 4 ohm load per channel, but not all are 2 ohm capable. Increased resistance (ohms) will reduce power output, but this may not actually be a bad thing considering you're running some very small speakers. If you do this all the speakers on each channel need to be the same size and model, I wouldn't mix and match them.
My main concern still is really just fading and setting the soundstage up properly, not sure how that's going to work running 6 rear channels and 2 front channels off of one four channel amp. That's asking a lot from very little equipment. It will technically work, all your speakers will play sound, but my fear is that there will be no real way to balance the sound towards the front properly.