Sennheiser XSW1 Wireless Earset Microphone System Kit (Beige, A: 548 to 572 MHz)

This is a single receiver system that works with only one transmitter. If you require additional mics, then you would use full systems for each mic set to different frequencies.

The Sennheiser XSW 1 DUAL 2-Person Wireless Omni Lavalier Microphone System Kit (A: 548 to 572 MHz) does not have an SD card slot for recording. You would connect the XLR outputs on the back, into an audio recorder, to be able to get the audio onto an SD card.

I would recommend doing a test recording with the mic starting off with the default sensitivity setting. Experiment with the settings as well as the positioning of the mic to find the combination that works best for you. When you do the test recordings, you can say which setting you are using for the sensitivity level and where the mic is placed. Just speak and record, and that way you can easily listen back and compare the audio clips without having to remember how everything was set up.

I'm sorry, but that system is only available within one frequency range. For more available ranges, I would recommend considering the more professional EW 100 G4 systems, like these: https://bhpho.to/3a3qpaM

Just to clarify, I believe the question is asking, bases on buying two of these kits, if you can use all four mics. I believe you can only use either the handheld or the lapel as there is only one receiver. So the question should not be if their is interference, it should be can the reciever take both mics, and I believe the answer is no.

"Change one to a different frequency"

Yes, you can use both transmitters at the same time with the Sennheiser EM-XSW 1 receiver. The receiver has two separate channels so it works with two wireless transmitters/microphones at the same time.

The Sennheiser XSW system will give you about 75 to 100 feet operational distance. Line of sight.