The purpose of two antennas is to minimize the multi-path cancellation effect. The receiver automatically switches to whichever antenna is receiving the strongest signal. If several FM microphones are used at the same time, each must operate on a different radio frequency. This means they operate on a very high radio frequency around 900Mhz. Usually they will provide better performance than the VHF units.
Omnidirectional microphones hear or pick up sound from all directions equally.
Omnidirectional microphones cause feedback easily. Omnidirectional microphones sometimes sound more natural for recording purposes. A Laveler microphone is a small microphone which usually has a clip to attach it to the performer's clothing. FM Laveler microphones provide the greatest freedom of movement. Laveler microphones usually do not sound as natural as hand held mikes and are less desirable for singing.