Mr. Dursley hummed as he picked out his most boring tie for work, and Mrs. Dursley gossiped away happily as she wrestled a screaming Dudley into his high chair.
as 是连词,引导的从句没有伴随状语从句的说法。这是时间状语从句,跟主句同时发生,翻译为“ 一边...(从句),一边....(主句)”。
后半句前面有一个并列连词 and,说明它是第二个并列分句。哪里来的伴随状语?建议网友认真读一下句子的结构和分类。