Until we have formulated a specific response to Mr. Al-Kadhi, the following links should give enough food for thought.
In particular, it is a logical fallacy to draw conclusions from modern English usage, or even classical Arabic (AD 600) that therefore Biblical Hebrew in 1200 BC also has the same grammatical features. Plainly, there is no plural of respect in Biblical Hebrew. This is admitted even by the Jewish rabbis. Maybe it exists in the Qur'an but this is irrelevant for the Hebrew Scriptures.
The following articles talk at some length about Hebrew grammar and give quotations from rabbinical scholars on this issue:
More discussion on this topic is found in the article, A Brief Rebuttal to Anti-Missionary Attacks on the Trinity.
Not only is a plural of majesty unattested for in Biblical Hebrew. According to Dr. Gleason Archer, Prof. of Ancient and Semitic Languages, there is no known ancient language of the BC period in which there is found the usage of a plural of majesty. (Source: What are the truth claims of Islam versus the truth claims of Christianity? Part 1: The concept of God in Islam and Christianity, transcript)
Al-Kadhi seems to be confused even about the plural of respect in Arabic as can be seen in his response to a problematic Qur'anic passage.
The Rebuttal to "What Did Jesus Really Say?"
Answering Islam Home Page