Online Resources ??

I am doing some family research for my sister-in-law, whose ancestors are from Friesland as well.
Her grandparents names were Wolter Bonnema and Aaltje van der Heide.
According to Graftombe - Wolter was born in 1903 and Aaltje in 1905 - the family itself came from the Tietjerksteradeel area of Oenkerk. My problem is, that those birthregisters stop at 1902.
Are ther other online resources where one can look up later dates?
By looking through the archives online I can venture a guess as to who the parents are, but is there a way to know for sure?