Volume 1 will have:
Mega Man Battle Network
Mega Man Battle Network 2
Mega Man Battle Network 3 Blue
Mega Man Battle Network 3 White
Volume 2 will have:
Mega Man Battle Network 4 Red Sun
Mega Man Battle Network 4 Blue Moon
Mega Man Battle Network 5 Team ProtoMan
Mega Man Battle Network 5 Team Colonel
Mega Man Battle Network 6 Cybeast Gregar
Mega Man Battle Network 6 Cybeast Falzar
If I remember. Each game have different set of Navi (which is the Pokémon) of this game as featured. While for 6 is different last boss and features