I remember reading this book a long time ago, but I remember there being a Kangaroo warrior, a lizard guy, and a few humans. I think they go into some sort of tower and deal with demons. I think the people are trying to rescue a princess or a wizard, something like that (I know that narrows it down by a lot!)
I know it's not warriors of virtue, as that was the first result when searching for 'kangaroo warriors'.
Also, not a spell singer novel. It came out in the mid 80s, and I believe had a tie in with other media as well.