Both Johan and Johalva join the liberation army.
Somehow everyone is recruited in FE5.
Lalum, Elphin, Batre and Echidna all join Roy and he goes through both Sacae and Ilia on his way to Bern.
Galle survives and joins Roy.
Geitz, Wallace and Harken and Karel are recruited.
Karel begins to reform after killing Guy between FE7 and FE6 and feeling horrible about it.
Chrom hires both armies in FE13
There were actually two My Units in FE12 (Kristina and Christian?) and they were twins. The very few historians that do know about Kris think that there was only one and are unsure if he/she were male or female.
FE13 Avatar is the descendant of the FE12 male avatar and Katarina.