What is the ruling on semen discharged after pre-seminal fluid, and is it considered impure due to its mixing with pre-seminal fluid, and do the man and his wife become impure by it?

If semen mixes with madhy (pre-seminal fluid), and the latter is impure, then the semen also becomes impure, prioritizing the aspect of impurity. In this case, all of it becomes forbidden if it is not clearly distinguishable.