Complex sentence: The orchestra was later conducted by Ole Olsen, Johan Selmer, Iver Holter and Otto Winter Hjelm, and it was under Holter that the orchestra was fused together with Christiania Theatre Orchestra, which was on the verge of reductions.
Split into simpler sentences: The orchestra was later conducted by Ole Olsen, Johan Selmer, Iver Holter and Otto Winter Hjelm. Under Holter, the orchestra was merged with the Christiania Theatre Orchestra, which was on the verge of reductions.