Why does Kanga needs Scrappy?You might want to know that you cannot transfer them at level 100 as the nature will be fixed to Hardy.
A mono gen 1 team is quite unrealistic though. Most need egg moves to be relevant or are not good with their HA.
For example, Kangaskhan wants Scrappy to be strong on tree.
Anyways I trade them over at Level 99 with the correct amount of EXP to fulfill the EXP%Modulo blabla formula
And I level them up with Rare Candies