Following up trupheus suggestions. (Sharing his sentiment that it should be a province game rather than political one. Gameplay would more balanced and welcoming for new and lone players)
- Stop ability to send aid outside your province. (Use the marked for that not a multi)
- Pre only valid when an attack is made by a province team mate. ( take the relevance of too many provinces joining together and destroying gameplay joy)
- Friendly spells to be limited in being casted on province members. ( Use the market for that not a multi)
- Province kingdoms cannot attack each other. (Avoid castle passing)
Just some lines of thought. Feel free to ignore