respected maam,

the sentence " The neighbours or Dev (is/are) responsible for littering the ground"

"Twenty-five years (has/have) passed since their marriage"

kindly tell the correcte form of verb

In the first sentence, if you are using neighbours you will have to put 'are' and if you are using Dev the you have to put 'is'. While in the second sentence their is no alternative and you have to put 'have'.

The neighbours or dev is responsible for littering the ground.

Twenty-five years have passed since their marriage