Hiya!
I run the animals with their stats high on the list of important things to consider regarding the Druid's commands. Yes, the animals are "fey spirits", but figure they are the same 'animal type', but just a fey from the Happy Hunting Grounds or, what is it..."Feywild" or something? Anyway, a Summoned Panther still has the stats of a Panther; meaning it has a 3 Int. It can follow
simple commands. I figure anything that a well-trained dog could do, it can do. So "Stay", "Guard", "Fetch", and slightly better like "Go Home", "Carry this", and such. But there is no way in H-E-Double-Hockey-Sticks I would let the Druid player get away with "Protect the entrance here from any goblins or bad guys. Come get us if you see more than 4 getting close to you". If an Elk was given that command...it'd walk over the the entrance and start eating grass. That's about it. It might bellow if something got close to it, like a squirrel or something, but numbers of creatures, specific creatures and any 'additional info' past the first few words would be lost/forgotten by it in short order. It's an Elk with a 3 Int. It's not Hannibal with the linguistic capabilities of Shakespear.
So...yeah. Never been a problem in my games. I should also note that I DM in a very "INTENT of the PLAYER" sort of way. If I see a player trying to use Summon Animals to basically "avoid any challenge/danger...and then claim all the rewards", then I am
very harsh in my ruling. But if a player uses it to add a cool element to the feeling of the game or the story at hand, without regard for trying to "game the system", then I am
very lenient. "I'll summon 8 animals and tell them to attack the bandits! We can then go in and clean up!"...er...not gonna work out very well. "I'll summon an animal to take the note to Amrissa"...will work out pretty much as desired. This usually means that it ends up somewhere in the middle. "I'll summon some animals to attack as a distraction so that we can get closer to them before they notice us"...yeah, that will likely work decently enough; the animals aren't doing "all the work", so to speak.
It's a fine line and it is only this way because I've been playing with most of the current group for almost two decades now. We "know" how we play and what is/isn't considered 'gaming the system' (or, in our parlance, "shenanigans").
Once you (OP) start to make consistent rulings on what a spell is likely to be 'able to accomplish', the group will start to jell and you won't have this type of "gaming the system" situations come up very often at all. In the end, IMHO, the game is better for it.
YMMV.
^_^
Paul L. Ming