Like their modern day counterparts, the Delightful Children From Down The Lane, they frequently celebrated their birthday and prepared a delicious cake which they refused to share with anyone else. The cake's recipe was kept by their mother, who is Father's great-grandmother. When the KND attacked the Alamode to get the recipe, Numbuh 19th Century set off a defense mechanism, which caused a nuclear explosion of ice cream that froze close to five thousand operatives (all of whom had to be decommissioned after being thawed, as they were technically over 13). One of them could be Grandfather's mother.
The triplets seem to be based on the twins from The Shining .
It is possible that one of them is Grandfather's mother. If this is the case, it may mean that one triplet can act on her own accord, meaning they may not be one entity like their later descendants.
Since their bloodline had produced Father in the current time, it is reasonable to assume that the triplets (and possibly their mother) were able to escape before the flash-freeze.
Their mother is all black and red, which would mean she possibly had thermal-based abilities similar to Grandfather and Father.