The parental bond cannot be broken even if one tries.

The parental bond cannot be broken even if one tries. 
親子の縁は切っても切れない。

There will still remain a strong bond between the two companies. 
両社間の強い結び付きは引き続き変わらないことでしょう。

bond between father and daughter
《a ～》父と娘の絆

bond between father and son
《a ～》父と息子の絆

bond between husband and wife
夫婦間の絆

bond between lord and vassal
《the ～》君臣［主従］の結び付き