I think this might be Carol Kendall's The Gammage Cup (1959) - which appeared here in the UK as The Minipins. https://en.wikipedia.org/wiki/The_Gammage_Cup

The story starts in a fictional valley named the Land Between the Mountains. It is surrounded by four mountain ranges: Snowdrift to the north, Frostbite to the south, the Sunrise Mountains to the east and the Sunset Mountains to the west. This valley is populated by twelve villages of Minnipins, a race of industrious "little people" rather like hobbits.... who, despite inner divisions, must unite to defend their village and the valley in which they live against an evil race of humanoid creatures called the Mushrooms or Hairless Ones.

These Mushroom creatures attack them through passages in the mines in the surrounding mountains and there are the battles in caves that you describe. There is one main character, Muggles (female), and a group of other 'misfits' from the village who group together to save it from the invaders. As I remember it, the skill posessed by each of this group is more in the nature of a talent they come to recognise than a magical skill, although they do have a magic sword that glows when the enemy are near. The bits that fit less well with your description are that I think this has always been regarded as a children's book and, although it has been regularly reprinted, it is much older than the 1990's.

I think this might be Carol Kendall's The Gammage Cup (1959) - which appeared here in the UK as The Minipins.

The story starts in a fictional valley named the Land Between the Mountains. It is surrounded by four mountain ranges: Snowdrift to the north, Frostbite to the south, the Sunrise Mountains to the east and the Sunset Mountains to the west. This valley is populated by twelve villages of Minnipins, a race of industrious "little people" rather like hobbits.... who, despite inner divisions, must unite to defend their village and the valley in which they live against an evil race of humanoid creatures called the Mushrooms or Hairless Ones.

These Mushroom creatures attack them through passages in the mines in the surrounding mountains and there are the battles in caves that you describe. There is one main character, Muggles (female), and a group of other 'misfits' from the village who group together to save it from the invaders.

As I remember it, the skill posessed by each of this group is more in the nature of a talent they come to recognise than a magical skill, although they do have a magic sword that glows when the enemy are near. The bits that fit less well with your description are that I think this has always been regarded as a children's book and, although it has been regularly reprinted, it is much older than the 1990's.