Grading: The report is sahih, except that the mention of 'Ali (may Allah be pleased with him) in it is gharib; for what is preserved from him is that he did not make the full brothers share with the maternal brothers, as will be quoted from the scholars below.
Technical note / Defect ('illah): This chain is weak: Ibn Abi Layla (Muhammad bin 'Abd al-Rahman) has a poor memory (sayyi' al-hifz), and al-Sha'bi's narration from these Companions is mursal.

Reference / Source: Sa'id bin Mansur recorded it in "al-Sunan" (23) and al-Bayhaqi in "al-Sunan" (6/256) through the route of Hushaym, from Ibn Abi Layla, from al-Sha'bi: "that 'Umar and Ibn Mas'ud (may Allah be pleased with them both) made them share." It does not mention 'Ali.

Reference / Source: Al-Bayhaqi (6/256) recorded it through the route of Yazid bin Harun: Muhammad bin Salim informed us, from al-Sha'bi, who said: "'Umar and 'Abd Allah said", and he mentioned it.
Technical note / Defect ('illah): Muhammad bin Salim (al-Hamdani al-Kufi) is weak.

Reference / Source: Something similar was recorded by 'Abd al-Razzaq (19009), Sa'id bin Mansur (20, 21), Ibn Abi Shaybah (11/255, 256, 258), al-Darimi (2924), al-Baghandi in "Fara'id al-Thawri" (22), and al-Bayhaqi in "al-Sunan" (6/256) and "Ma'rifat al-Sunan" (12657), through the route of Ibrahim al-Nakha'i, from 'Umar, Ibn Mas'ud and Zayd (may Allah be pleased with them).
Grading: Its chain up to al-Nakha'i is sahih.
Technical note / Defect ('illah): The narration of Sa'id bin Mansur (21) and the second and third narrations of Ibn Abi Shaybah add: "and 'Ali would not make them share." Ibn Abi Shaybah said: "This case is worked out from six shares: for the husband one half, three shares; for the mother one sixth (one share); and for the maternal brothers one third, which is two shares."

Reference / Source: Al-Bayhaqi recorded in "al-Sunan" (6/255) through the route of Sa'id bin al-Musayyab: "that 'Umar made the full brothers and the maternal brothers share in the third."
Grading: Its chain up to Sa'id is sahih, but there is disagreement over whether Sa'id heard from 'Umar.

Reference / Source: Sa'id bin Mansur (24) recorded something similar in brief through the route of Ibn Sirin, and al-Darimi (2929) through the route of Fayruz, both of them from 'Umar.

Reference / Source: It was recorded by 'Abd al-Razzaq (19005), Sa'id bin Mansur (62), Ibn Abi Shaybah (11/255), al-Darimi (671), al-Bukhari in "al-Tarikh al-Kabir" (2/332), Ya'qub al-Fasawi in "al-Ma'rifah wa al-Tarikh" (2/223, 224), al-Daraqutni (4126), al-Bayhaqi in "al-Sunan" (6/255) and "al-Ma'rifah" (12656), Ibn 'Abd al-Barr in "Jami' Bayan al-'Ilm" (1670) and al-Khatib in "al-Faqih wa al-Mutafaqqih" (1213), through the route of Wahb bin Munabbih, from al-Hakam bin Mas'ud al-Thaqafi (some said: Mas'ud bin al-Hakam), who said: "'Umar bin al-Khattab gave a ruling concerning a woman who died leaving her husband, her mother, her maternal brothers and her full brothers; 'Umar made the maternal brothers and the full brothers share in the third. A man said to him: You did not make them share in such-and-such a year. 'Umar said: That was according to what we ruled then, and this is according to what we rule now."
Grading: Al-Dhahabi said in the biography of al-Hakam in "Mizan al-I'tidal": "This chain is acceptable (salih)."

Reference / Source: 'Abd al-Razzaq (19006) recorded through the route of al-Zuhri that 'Umar bin al-Khattab said: "When nothing remains but the third, between the full brothers and the maternal brothers, they share in it, the male receiving the same as the female."

Reference / Source: Sa'id bin Mansur (27) and al-Darimi (2927) recorded through the route of Abu al-Zinad, who said: "Zayd (bin Thabit) used to make them share."

Important point: As for what has been reported from 'Ali (may Allah be pleased with him), that he did not make them share:

Reference / Source: 'Abd al-Razzaq (19010, 19011), Sa'id bin Mansur (21, 22, 26), Ibn Abi Shaybah (11/258, 259), al-Darimi (2925, 2926), Ibn al-Mundhir in "al-Awsat" (6784, 6785, 6787) and al-Bayhaqi (6/256, 257) recorded through various routes from 'Ali (may Allah be pleased with him) that he did not make (the full brothers) share (with the maternal brothers).

Technical note / Defect ('illah): Waki' said (as in the narration of Ibn Abi Shaybah): "There is none of the Companions of the Prophet (peace and blessings be upon him) about whom reports do not differ on the sharing, except 'Ali, for he did not make them share." Al-Bayhaqi said: "This is well known from 'Ali (may Allah be pleased with him)."