-----of them ----- ----- take a walk in the park.(他们俩以前都不去公园

表示“两者都不”要用neither;
Neither of them used to take a walk in the park.
each,every,either,neither,much,one,many a引导的句子用单数
主语由either…or,neither…nor,not only…but also…连接,动词与后面主语一致.