Reb Eliezer, you quoted the Mishna Brurah. However, this is actually a great machlokes haposkim, with MANY poskim clearly ruling that one is allowed to ask deceased tzadikim (their neshamos) to intercede on their behalf.
For example:
חמדת ימים, פחד יצחק, פרי מגדים, מנחת יצחק, בצל החכמה, חוות יאיר, מנחת אלעזר, יראים, ועוד ועוד
These poskim explain clearly why this is not דורש אל המתים.
The poskim who don’t allow it have many מאמרי חז”ל to answer, where it clearly mentions תנאים ואמוראים (and Kalev) who went to קברים and spoke to the מת with various requests.
סוטה לד, ב. פסיקתא רבתי ג. ברכות יח,ב. חגיגה כב, ב. ועוד ועוד
And of course the Zohar.
Everyone should follow their minhag and their rov.