Question

you as well as he are to blame for the accident 那个you as well as he are to blame for the accident

Answer 1

you as well as he are to blame for the accident
你和他都要对这次事故负责。
as well as
1. 除…之外(也)，同…一样(也)，和，也，还
2. 与…一样(程度)
3. 既…又… [见well]
4. 与…相同；不亚于…
5. 此外，也
be to blame
该受责备(或指责)的；应负责任的；(是)某种不良后果的原因

Answer 2

这里主语为You, 后面用are没错。 to blame 用主动式表被动也很地道。
此句没问题

“不仅他而且你也得对此次事故负责。”

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