I am looking at doing home recording on my 13" Macbook Pro (mid-2012) and was wondering if it would be possible to use a Focusrite 2i2 and a Focusrite 2i4 at the same time so that I could have 4 mics go into the preamps and have midi all at the same time? Logic Pro X is the recording program I normally use.
Hardware wise, you might end up with some differences in latency that could result in slight differences in the timing of the recordings, but you could probably adjust for that if it is an issue, so I wouldn't expect it to be too major since you are using such similar hardware. (Note, I don't have direct experience on that, but I don't see a technical reason that I'd expect it to be a problem, at least for simple stuff.) If you feel like upgrading later, you can use interfaces that support a word clock signal and they will be able to keep themselves exactly in sync using that word clock, but with your current hardware, that isn't an option.
Mac OS also provides support for aggregate devices that will combine the interfaces in to a single virtual interface that you can use in Logic Pro X. More details about how to do so can be found directly from Apple's documentation here. If the link goes bad, you simply need to go to the Sound options, create a new aggregate interface and add all the channels from the devices you want to use to it.