Hey there!
In Survival, If you right-click your minion, a user interface will pop up in which you can place the spawner to have the minion automatically slay those mobs and store the drops for you to sell. Just make sure the minion is consistently supplied with sweet berries, or else it won't work.
As for spawner stacking, placing multiple spawners of the same type in a given chunk will automatically stack those spawners up to a maximum of 64.
If you have any more questions, feel free to contact me on Discord @ pandabees or in-game (IGN: pandabees)
You can find more information on minions here:
Survival - Items | ManaCube Official Wiki |
Minions | ManaCube Official Wiki