Your team is not only badly balanced, but poorly trained. Cynthia has almost level 70 Pokemon; your highest is level 57 and your lowest is level 44. I suggest first getting a team that uses natural advantages such as being two types at once to its best intrest; i like Abomasnow because it takes care of Bertha's weakness for grass and any strong dragon types, plus its Snow Warning can be rather useful, and Weavile's nice as well, since it also has Ice attacks for use against Dragon types and it's a Dark type, good for the 4th Elite. After balancing your team, train, and train hard. You can't just waltz in there and out a Champion the next. They'll mop the arena floor with you.
But then again, this is me writing at an absurd time in the morning, so any problems with my love for Weavile and Abomasnow in this and you can let me know. Mmkay, I need to sleep.