Authentic Descriptions of Munkar and Nakeer

Firstly: 

It is narrated in saheeh reports that the
two angels whose task it is to question the deceased are black and blue, and
one is called al-Munkar and the other is called al-Nakeer. 

Al-Tirmidhi narrated that Abu Hurayrah
(may Allah be pleased with him) said: The Messenger of Allah (peace and
blessings of Allah be upon him) said: “When the deceased – or one of you –
is buried, there come to him two black and blue angels, one of whom is
called al-Munkar and the other al-Nakeer. They say: ‘What did you say about
this man?’ and he says what he used to say: ‘He is the slave of Allah and
His Messenger. I bear witness that there is no god but Allah and that
Muhammad is His slave and Messenger.’ They say: ‘We knew that you would say
that.’ Then his grave is made spacious for him, seventy cubits by seventy,
and it is illuminated for him. Then it is said to him: ‘Sleep,’ and he says:
‘May I go back to my family and tell them?’ They say: ‘Sleep like the
bridegroom who will be woken by none but the dearest of his family to him,’
until Allah raises him from that resting-place of his.” 

But if he is a hypocrite he says: ‘I heard
the people saying something so I said something like what they said. I do
not know.’ They say: ‘We knew that you would say that.’ Then it is said to
the earth: ‘Squeeze him.’ So it squeezes him until his ribs interlock, and
he will continue to be tormented therein until Allah raises him from that
resting-place of his.” 

This hadeeth was classed as hasan (sound)
by al-Albani in Saheeh al-Tirmidhi. 

With regard to the hadeeth of ‘Umar  (may
Allah be pleased with him) to which you refer, it was narrated via da’eef
(weak) isnads (chains of narration), such as the mursal (one whose chain
stops at before reaching the companions) report narrated by ‘Abd al-Razzaq
in his Musannaf from ‘Amr ibn Dinar, according to which the Prophet (peace
and blessings of Allah be upon him) said to ‘Umar (may Allah be pleased with
him): “How will you deal, O ‘Umar, with the two testers in the grave, when
they come to you digging the earth with their eyeteeth, stepping on their
hair (because it is so long), their eyes like dazzling lightning and their
voices like deafening thunder, with a whip so heavy that if the whole world
were to gather together to lift it, they would not be able?” ‘Umar (may
Allah be pleased with him) said: “I will be as I am today”. He said: “As you
are today?” He said: “Then I shall take care of them for you, in sha
Allah.” 

Al-‘Iraqi said in Takhreej al-Ihya: This
was narrated like this, as a mursal report, by Ibn Abi’l-Dunya in Kitab al-Quboor,
and its men are thiqat (trustworthy). Al-Bayhaqi said in al-I’tiqad: We have
narrated it via a saheeh isnad in a mursal report from ‘Ata’ ibn Yasar. 

I say: Ibn Battah narrated it in a mawsool
report (reaching the Prophet) in al-Ibanah, from the hadeeth of Ibn ‘Abbas
(may Allah be pleased with him), and it was narrated by al-Bayhaqi in al-I’tiqad
from the hadeeth of ‘Umar (may Allah be pleased with him), but he said it is
ghareeb (strange) with this isnaad, which was narrated only by Mufaddal.
Ahmad and Ibn Hibban also narrated from the hadeeth of ‘Abd-Allah ibn ‘Umar
 (may Allah be pleased with him) that ‘Umar (may Allah be pleased with him)
said: “Will our awareness be restored to us?” He said: “Yes, just as you are
today.” ‘Umar  (may Allah be pleased with him) said: “Then I will throw a
stone in his mouth.” end quote. 

Professor Fareej ibn Salih al-Bahlal said
in his commentary on al-I’tiqad by al-Bayhaqi, after referring to the da’eef
isnad (weak chain of narration): Perhaps by virtue of these isnads and
corroborating reports its isnad may be hasan. End quote. 

Secondly: 

The questions which the angels put to the
deceased in his grave are: Who is your Lord? What is your religion? Who is
this man who was sent among you? 

See also question no.

10403 and

22203 

And Allah knows best.