Is it obligatory to wash the urinary meatus and the two sides and rub them when urine mixed with prostatic fluid is discharged, or is it sufficient for the impurity to be removed by wiping with water? And what is the ruling on the finger touching a part of the inside of the penis?

You must abandon obsessive thoughts and turn away from them. When cleaning oneself after urinating and defecating (Istinja'), one should start with the front private part, then the back private part. Only the soiled area must be washed with water until the impurity itself and its trace are removed. A strong presumption of cleanliness (ghalabat al-dhann bi al-inqa') is sufficient for this. Wiping with water is not enough to purify from impurity.