Complex sentence: Finally the singer HALNA was chosen to be a part of HAL and they signed a deal with record label Avex Trax, since then they stopped momentaly their group as arrangers after the work with "Grip!" from Every Little Thing.
Split into simpler sentences: Finally the singer HALNA was chosen to be a part of HAL and they signed a deal with record label Avex Trax. They temporarily stopped their group as arrangers after the work with "Grip!" from Every Little Thing.