他们被几个人用枪指着 用英语怎么说

They are being pointed at by several people with the gun.

They are being pointed on by several guns.

被几把枪指着，就是几个人。

They are pointed at by several guns.

They were being held by several pointed guns.

They were pointed at by several persons with guns.

这是主动句：A few people are pointing their guns at them

那么根据你的要求改成被动句就是：
Guns are being pointed at them by a few people.