The plan was not that complicated. They would split into two teams, the advance and the support team. Solomon and Kovu were the advance. They would infiltrate the city and rescue Emberle before her execution. That part was easy. Solomon used and skycraft and Kovu shifted into a bird to get over the wall. Greed, Tia and Oriella as the support were to wait to defend the advance team against the army of angels that would be tailing them when they came out and make for a clean escape.
They weren't expecting any arcanians where archangels were involved so they had one less thing to worry about. Really, not that complicated.