Let's say I have two lairs, one with 2 crawlers and one with 4 grubbers. Do I spawn 4 crawlers? (I have 2 crawlers total, but 6 minions on the tile)
To my knowledge, there is no official ruling of this sort of thing. I would treat "special events" as one global thing. If you have that many minions total, spawn four additional minions. Two of each type if you still had two lairs. If you only had one grubber lair, with two crawlers and two grubbers left, spawn four extra grubbers.
And if I have a lair with 2 grubbers and a hunting pack of 5 grubbers, do I spawn 4 grubbers?
Yes. It doesn't matter where the minions come from after you set up the tile.
I would assume the event is for creature type, so in the first situation I would spawn and in the second not. Is this correct?
It is only my opinion, but I think I would interpret it as above.