What is the ruling on partnering with brothers to build a joint factory, on the condition that each partner has his independent factory within the same building, and if a Sharia-compliant order comes, they participate in it, otherwise they do not?

It is understood from the question that each partner has his own share, and that the partnership contract entails accepting and working on orders. The questioner stipulated to his partners that the company's field of work must be permissible, so he will not execute an order for a forbidden entity and will not share in its profit. There is no objection to this; for the contract is the law between the contracting parties, and it is not permissible to accept a forbidden order or to participate in its execution. The questioner should advise his two brothers not to commit forbidden acts or assist in them.