Sentence:  Both paternal and maternal <WSD>grandfathers</WSD> were highly involved in various facets of adolescents' lives, with maternal <WSD>grandfathers</WSD> providing more support in generalnb.... It was found that, on average, maternal <WSD>grandfathers</WSD> were more involved with adolescent grandchildren than paternal <WSD>grandfathers</WSD>. Adolescents also felt closer to maternal <WSD>grandfathers</WSD> compared to paternal <WSD>grandfathers</WSD>. This may be explained by the more regular contact and closer geographical distance between these <WSD>grandfathers</WSD> and adolescents. 
Meaning of the word marked with <WSD> tags:  A father of someone's parent. (from 15th c.)