we want to London by the train at nineteen minutes past eight这句话对吗 我们要乘8：19的车去伦墩

错了，We want to go to London by the train at seven past eight p.m.

不对,应该用将来时态。
We will take the train to London at eight nineteen/nineteen past eight .

we want catch the train to london at nineteen past eight

不对，怎么能说want to London呢？

表达用什么交通工具,采用什么方式要用by train,不能加冠词.

We want to go to London by train (that)leaves at nineteen past eight.