Is it permissible for me to continue in the company based on my capital contribution and my son's labor contribution, while I receive a fixed monthly amount?

The agreement in the partnership must be based on a common share of the profit that both parties accept, and it is not permissible to give the worker a fixed amount. If no share of the profit is specified for the worker, then all the profit belongs to the owner of the capital, and the worker is entitled to a wage equivalent to that of his peers. Therefore, the partnership must be rectified by agreeing on a known percentage of the profit for each of you. As for the past period of the partnership, its profit belongs to you, and your son is entitled to a wage equivalent to that of his peers.