I have 7 devices plugged into my development machine.
Normally I do adb install and can install to just a single device.
Now
well its simple you can create a installapk.bat file that can do the job for multiple apk to multiple connected devices open installapk.bat with notepad++ and copy paste this code
FOR /F "skip=1" %%x IN ('adb devices') DO start adb -s %%x install -r Facebook.apk
FOR /F "skip=1" %%x IN ('adb devices') DO start adb -s %%x install -r Instagram.apk
FOR /F "skip=1" %%x IN ('adb devices') DO start adb -s %%x install -r Messenger.apk
FOR /F "skip=1" %%x IN ('adb devices') DO start adb -s %%x install -r Outlook.apk
FOR /F "skip=1" %%x IN ('adb devices') DO start adb -s %%x install -r Viber.apk
FOR /F "skip=1" %%x IN ('adb devices') DO start adb -s %%x install -r WhatsApp.apk