another thing you can do is add a compressor (audio effect) to a "tag" and then play the sounds through that tag. this will not totally fix the volume but it will help a lot.
the compressor will act as a "limiter" and will try to squash the volume if it gets too loud.
play around with the Threshold (lower it) to get it right. And set the Knee to 0 (so its applied right away)
EDIT: also set the "attack" to something really short like 1 - but it all depends on your sound