Simply what family structure I imagine with certain characters
Ludwig
Father: Klaus (HRE)
Grandfather: Sven (Germania)
Step-Mother: Maria "Ria" (Fem!Austria)
Step-Brother: Roderich (Austria)
Brother: Gilbert (Prussia)
Order of brothers (oldest to youngest): Gilbert, Roderich, Ludwig
Overall relationships: Ria and Roderich came into the Beilschmidt's lives fifteen years after the passing of their mother. With some difficulties Ludwig and Gilbert try and adjust to having another brother. Gilbert's relationship with his father and grandfather are strained enough and adding Roderich, who easily gets on his nerves, sets things down for the worse. Eventually all the arguments between everyone (except for Ludwig) drive Gilbert to adapting the habit of staying away from home for hours at a time. Roderich comes into the family a prodigy compared to Ludwig, who was already put on a high pedestal by his father and grandfather. Both Roderich and Ria push on him to call them "Mother" and "big brother" almost as soon as they move in, which Ludwig finds difficult to do.
Alfred
1)
Twin Brother: Matthew (Canada)
Mother: Alice (Fem!England)
Father: Francis (France)
Alfred and Matthew are practically inseparable. Being twins has let them form an almost spiritual bond that transcends any other relationship they have with friends, lovers or even their own parents. They'd do anything for each other at the drop of a hat. Even with Matthew's unfortunate circumstance of being cast under Alfred's shadow the two see each other on an equal level. Unfortunately this kind of relationship does not translate to their parents. Francis and Alice have been bickering and arguing with one another since the day they met. What the two thought to be love they found quickly wore itself out and brought them back to square one, bringing divorce and custody issues to the table.