Under California law, you may respond to a complaint by answer, demurrer or motion to strike and may file a cross-complaint, depending on the circumstances. You should consult with an attorney to discuss the particulars of your matter and for any specific legal advice.
If you and your brother are co-tenants of a present interest in the property either of you can seek a partition. If the property cannot be physically divided, it will be ordered sold by the Court. The plaintiff in an action for partition may recover costs of suit, which can include the cost of a title policy and an appraisal. With limited exceptions, there is no defense to a claim of partition and the plaintiff is likely to prevail . I would suggest that you attempt to settle the claim to avoid the cost of defending it. You might consider mediating the claim in the event you can't resolve it through direct negotiation. Perhaps one of you can buy the other's share net of brokerage commissions and other costs of sale. Good luck.