But then as Mama and Papa drove away, Sal burst into tears. A delayed reaction. It was as if something inside her suddenly broke or popped or was switched on. She was hysterical. Gabby, Billy, and even the Drop Sisters were powerless to soothe her.
The gushing of tears went on.
Billy couldn’t stand it. He put his hands over his ears. He’d gone from trying to be helpful, to being annoyed, to feeling angry. “CAN. WE. GO. NOW. PLEASE?” he repeated loudly over the relentless crying.
As for the bold sentence in the paragraph, I'm not very clear about its structure. Why is the first "to be" a to-infinitive, but the last two 'to's are followed by -ing form? What is the ellipsis of this sentence？