Saying khutbat an-nikaah before doing the marriage contract is Sunnah, because of the report narrated by Ibn Mas‘ood (may Allah be pleased with him), who said: The Messenger of Allah (blessings and peace of Allah be upon him) taught us to say tashahhud in the prayer and tashahhud in al-haajah…
Narrated by at-Tirmidhi (1105) and an-Nasaa’i (3225). Classed as saheeh by al-Albaani in Mishkaat al-Masaabeeh, no. 3149
See also the answer to question no. 88130
There is nothing wrong with the groom himself doing that khutbah.
Ibn Battaal (may Allah have mercy on him) said: The majority of scholars regarded it as mustahabb to say this khutbah in weddings. Maalik said: This is a long-established practice, and the shorter it is the better. Ibn Habeeb said: They used to regard it as mustahabb for the suitor to praise Allah and send blessings upon His Prophet, then propose to the woman.
End quote from Sharh al-Bukhaari (13/260)
Ibn Qudaamah (may Allah have mercy on him) said: It is mustahabb for the groom or someone else to give a speech before the proposal and acceptance, then the marriage contract is done after that.
It is mustahabb to recite the khutbah of ‘Abdullah ibn Mas‘ood, who said:
The Messenger of Allah (blessings and peace of Allah be upon him) taught us say tashahhud in the prayer and tashahhud in al-haajah …
End quote from al-Mughni (7/62)
As there is nothing wrong with the groom himself delivering khutbat an-nikaah, similarly there is nothing wrong with him directly addressing the guardian of the bride, so that the proposal and acceptance are exchanged: the proposal from the guardian and the acceptance from the groom. In fact this is the original format, and there is only a need for someone to do the marriage contract or to prompt the words because many people are ignorant of such matters and have little knowledge of the Sunnah in this regard.
As-Saawi (may Allah have mercy on him) said:
“It is recommended to give a speech” – with a rhyme and rhythm to it, starting with praise of Allah and the twin declaration of faith, including a verse in which there is the command to fear Allah, and mention of the purpose of the occasion.
“when proposing” i.e., when proposing marriage.
There should be “another speech when doing the marriage contract.” But the one who is to give the speech first when proposing is the suitor, who should say, after praising Allah and reciting the twin declaration of faith: To proceed: our aim is to join you and be your in-laws and part of your family – or words to that effect.
Then the guardian should say, after praising Allah: To proceed: we have accepted you and your proposal, and have accepted you as one of our family – or words to that effect.
The one who should give the speech first when doing the marriage contract is the guardian, who should say: To proceed: I give my daughter [or the woman who appointed me as her proxy], So and so [mentioning her by name] in marriage to you, in return for a mahr of such and such. After that, the groom says: I have accepted your giving her in marriage to me. The proxy of the groom says: I accept her marriage to the one whose proxy I am.
End quote from Haashiyat as-Saawi ‘ala ash-Sharh as-Sagheer (2/338)
With regard to writing the official documents, the only purpose behind that is documenting what has happened and guaranteeing people’s rights. Whoever does this registration of the marriage, it does not matter, and that has no impact on the validity or otherwise of the contract.
For more information, please see the answer to question no. 104662
And Allah knows best.