I strongly suggest using a single sound card instead of multiple USB microphones or sound cards. For an application like sound location, it is essential that the samples from the different microphones are recorded at exactly the same time. When using multiple devices, that's next to impossible; they will be slightly out of sync when the recording starts, and because their sample rates are not exactly the same, after some time the time difference becomes substantial. This can be counteracted using adaptive clock synchronization and adaptive rate resampling (see alsaloop for an example) but you will never obtain the precision a single sound card can get you.
So this means either using the stereo input of a standard sound card and dealing with the ambiguities this introduces or using a (USB) sound card that has 4 (microphone) inputs. Also a tip on the microphones: get omnidirectional ones, it makes the samples much easier to compare.
I'm not aware of the kind of the kind of software you're looking for, but directly working with ALSA is not too difficult; ALSA comes with great examples and audio data is relatively easy to work with compared to image data.