Kotlin synthetic extension and several include same layout

As a general rule of thumb, you should not construct layouts that end up having multiple views with the same id - for this very reason.

But, to solve your problem: Instead of importing

kotlinx.android.synthetic.main.layout.day_row.*

you can import

kotlinx.android.synthetic.main.layout.day_row.view.* (Notice the additional .view at the end).

This will import the views not as properties on the Activity/Fragment level, but instead as extension properties for View. That way, you can do it the way you want, assuming that day1 and day2 contain the views you want:

day1.dayName.text = "xxx"
day2.dayName.text = "sss"