Is the share of the questioner in the profits of a company in which he has invested considered lawful, given that there are other partners whose contributions might be from suspicious money?

The mixing of lawful and suspicious money increases the company's profit, and a portion of this profit comes to you. Therefore, be keen to partner with the righteous. If you become certain that their money is unlawful, then you must terminate the partnership, because partnering with them is an aid to sin and aggression. Allah Almighty says: "And do not cooperate in sin and aggression."