FE1: Cain and Abel
FE3 Book 2: Rody and Luke
FE4: Alec and Noish
"Third Cav"
FE1/DS: A bunch of people. Take your pick from Hardin, Vyland, Matthis, and Roshea
FE3 Book 2: Cecil
FE4: Ethlin's the only one I can think of, if not then you've got Finn/Lex/Sigurd to choose from
FE5: Carrion/Finn
FE6: Treck/Noah
FE7: Lowen
FE8: Franz
FE9: Makalov/Astrid
FE10: Makalov/Astrid/Titania/Geoffrey
FE DS: Frey