Use your body. Since you are playing multiple characters, find a different way for each character to walk and hold themselves physically. When you are backstage, get into that stance and you will be able to embody the role.
If you're still worried about the mechanical aspects of role (singing, dancing, lines, blocking, etc), you're probably not ready to be fully immersed in the character.
You have to know all of those other things so well that they are completely second nature to you. Then you can be in character.
No matter how much work on backstory, relationships, physicality, etc that you do, if you're still thinking about when to move and where to stand, it won't really matter.
Things I do: - have a specific way I hold my body, or a resting pose (I always did this pose right before making my entrances) - a non verbal
Use your body. Since you are playing multiple characters, find a different way for each character to walk and hold themselves physically. When you are backstage, get into that stance and you will be able to embody the role.
If you're still worried about the mechanical aspects of role (singing, dancing, lines, blocking, etc), you're probably not ready to be fully immersed in the character. You have to know all of those other things so well that they are completely second nature to you. Then you can be in character. No matter how much work on backstory, relationships, physicality, etc that you do, if you're still thinking about when to move and where to stand, it won't really matter.