The only iPad models to have four speakers are recent models of iPad Pro. Don’t be fooled by your iPad seemingly having four speaker grilles. Your iPad mini has only two speakers - not four. Other than speakers, dependent upon model, the grilles conceal other items - such as microphones and an air pressure sensor.
Recent models of iPad have one speaker at top and one speaker on the bottom edge of the iPad casing - such that when viewed in Landscape orientation, your iPad will have a left/right stereo pair.
You can verify and compare iPad specifications here:
Compare Models - Apple
As a point of interest, older models of iPad had two speakers on the bottom edge of the iPad - one placed either side of the Lightning port. For these models, with the iPad positioned in Landscape orientation, both speakers were to one side of the screen.