We have mini4L which includes 1x MAX98357a. But optionally, with a MAX98357a-breadboard, it can be extended with a second MAX98357a. So you could connect two speakers.
Yes.
#ifndef HEADPHONE_ADJUST_ENABLE
AudioPlayer_MaxVolume = AudioPlayer_MaxVolumeSpeaker;
// If automatic HP-detection is not used, we enabled both (PA / HP) if defined
#ifdef GPIO_PA_EN
Port_Write(GPIO_PA_EN, true, true);
#endif
#ifdef GPIO_HP_EN
Port_Write(GPIO_HP_EN, true, true);
#endif
#else
if (Audio_Detect_Mode_HP(Port_Read(HP_DETECT))) {
AudioPlayer_MaxVolume = AudioPlayer_MaxVolumeSpeaker; // 1 if headphone is not connected
#ifdef GPIO_PA_EN
Port_Write(GPIO_PA_EN, true, true);
#endif
#ifdef GPIO_HP_EN
Port_Write(GPIO_HP_EN, false, true);
#endif
} else {
AudioPlayer_MaxVolume = AudioPlayer_MaxVolumeHeadphone; // 0 if headphone is connected (put to GND)
gPlayProperties.newPlayMono = false; // always stereo for headphones!