I have Pokemon SoulSilver and I was wondering if this is a good party alakazam typhlosion steelix lugia and magnezone and what would be another good Pokemon to have in my party

That's a good party, id add a dragon and a water type to it. my choice would be Salamence or Rayquaza (if its on soul silver, not got tht far yet) and a Milotic or a Kyogre. Id then teach the water type ice moves to combat other dragons.