They often play chess after they have had supper.这里 have had supper.怎么理解

这里是强调两个动作的先后关系,即吃完了晚饭后再下棋.
由于是描述习惯或经常是这样做,因此分别用了现在时和现在完成时.这里是不是吃晚饭对下棋产生影响的

另外下面两个句子怎么翻译

1.他们经常在吃晚饭前要先下一盘棋。(还有chess是不可数名词，这里的一盘棋怎么处理)

2.他们经常是一边吃饭一边下棋的。They often play a game of chess before they have had supper.
They often play chess while having supper.