Question on speaking to those in the grave

 
wa alaykum as salaam wa rahma!

Thanks for your question and for the support! As for your questions, I would first like to highlight the reference. The passage from The Sincere Friend of the Qur´an reads as follows:

Then, he went to the grave of Allah’s Messengerﷺ and prayed beside it. Then, after completing his prayer, he said:"Peace be upon you, O Messenger of Allah! Peace be upon you, O Prophet of Allah! Peace be upon you, O best of Prophets and most honourable of Messengers! Peace be upon you, O beloved of Allah! This is the last time I will be in your city, and the last time I will be at your grave and pulpit!O my father, I was forced out! I travelled through the land as a captive, O Messenger of Allah! I ask you for intercession with Allah the Mighty and Majestic, to support me with the confidence of certainty and the glory of God conscious, and to grant me a martyrdom that will join me with my noble forefathers and my pure family!"

First, it mentions that the imam (as) went to the Prophet's grave which emphasises that following points:

• He deliberately went there with the intention of addressing the Prophetﷺ
• He is not shown to have addressed anyone else outside of the Prophet's sanctuary nor from another city or country. I don't know of any report in which he was said to have gone to Baqi' to address any of the other Ahl al-Bayt, upon them be peace, or at Kufa to address the Commander of Believers, upon him be peace. 
• He prayed beside it and nowhere else. Perhaps this emphasises the belief in seeking blessings by it (tabarruk). 

Second, as for the address itself, the following points can be extracted:

• He addressed the Prophetﷺ in the second person (ex. "...you..."). This could mean that he was confident addressing the Prophetﷺ with the idea that his greetings and address were heard and acknowledged.
• He said that it would be his last time in Medina and at the Prophet's grave, emphasising that--at least, apparently--the Prophetﷺ was unaware of such, thus negating the possibility of absolute ilm al-ghayb.
• Similarly, he informed the Prophetﷺ that he was forced out and exiled, thus negating the idea that the Prophetﷺ was conscious of such. If it were a proper address, such would imply obliviousness on the part of the addressed since it would be superfluous to assume that one would tell someone something that he already is aware of. 
• He asked for the Prophet's intercession, which proves that the intercession is not restricted to the Day of Judgement. This is because his asking for intercession, was connected to that which is to take place in this life. He asked for yaqeen, taqwa and shahaada, which are all relegated to this world's life. Imam al-Haadi (as) related in his Ahkaam that the Prophetﷺ said ((Whoever visits my grave will receive my intercession)) without specifying the hereafter. Perhaps the idea is that the one who visits his grave will receive his intercession at the time of the visit as well as on the Day of Judgement.  

All such points should address your main questions.

As for the potential charge of idol worship, such cannot be implied since the imam (as) was acting in Shari' parameters. He did not ask the Prophetﷺ to grant any of his needs or desires; rather, he simply employed him to intercede on his behalf. He did so in the proximity of the zareeh with the confidence that his request would be heard. I know of no such instance where the imam (as) made the same entreaty from Kufa or anywhere outside of the Prophet's grave.

Shirk, at least from my understanding, would be attributing the qualities of the Divine to the created. Responding to the dua is reserved for Allah according to the Qur´an (Ref. Q. 27:62 & 18:52). Even the belief in tafweed (Allah designating the power of answering prayers to His creation) does not relieve one of such charge since there is no definitive proof for such belief. 

Calling out to an individual from a great distance or another country with the idea that you will be heard, would not make much sense if the person were alive, let alone dead! Even if one were to argue that Allah can give the dead the ability to hear from great distances, such argument would not be justifiable because the issue is not related to whether Allah can do it rather, does He do it. Such would need proof from the Qur´an to justify it.

And Allah knows best!

IRS 
 

Thank you for your questions! 

From my understanding, the term dua has linguistic meanings and a technical meaning. Linguistically, it can refer to the meanings you mentioned, including 'to invite' 'to call' 'to invoke blessings for' etc. However, the technical meaning entails an act of worship in which one invokes another who has the independent ability to grant that which the invoker is requesting. That is the reason that the word is synonymous with 'prayer' [Cf. Q. 9:103].

As for whether it is an act or worship or anything else would more so depend on (1) who is being addressed and (2) whether this individual is believed to be able to grant the requestor his/her request. For example, if I were to invoke Allah to grant me children, with the belief that He can do so, it is an act of worship. If I invoke a dead imam to grant me children, with the belief that he can do so, it is an act of worship. Even if one takes the position that the dead imam is a means by which Allah grants me my request, it would still be considered an act of worship because of the one I am addressing. 

This is altogether different from invoking a live person to give me money or inviting a person for dinner, for example, because this gets into the linguistic meaning of dua, not the technical meaning.

Hopefully, this clarifies matters. And Allah knows best!

IRS

Thank you for your question! 

There would be no problem for one to request another to make dua for them. This request would not be considered dua as it requests dua. Requesting a living pious person to make dua for you would not be considered problematic, and it is only natural for one to do so. However, it may get problematic when crowding at the grave of a pious person with the assumption that such person can take the various requests being made simultaneously and make dua for each and every person. It is problematic because we have no textual proof for such.

And Allah knows best!

IRS