Guillaume II De Saint-Omer
Guillaume II was born in 1085.

 Melissende De Picquigny
Melissende was born in 1090.  Melissende is no longer alive.

 Guillaume III De Saint-Omer
Guillaume III was born about 1115.  He died about 1170.

 Mahaud De Saint-Omer
Mahaud was born in 1115.  She died at the age of 54 in 1169.