1b. The cost of a divorce varies greatly from case to case. Uncontested matters can resolve for around $2000 and heavily contested matters can go well into the tens of thousands. I would guess that the average divorce costs around $5000. The cost is mainly a reflection of the number of hours it takes to complete a case which can be affected by: the complexity of the marital property, child custody/visitation issues, child support, spousal support, the ability or inability to compromise between the parties, and the hourly rate and efficiency of the attorneys.
2. From the facts given, it is likely that the house will be deemed community property. If the home was bought during the marriage and paid for with community property funds, it is going to be community property. It does not matter who worked more or who paid a greater share of the mortgage.
3. In the context of divorce, what you and your sibling did has no relevance. If you're asking about something criminally-related, then I would need more information.