Gemara

52b (R. Yochanan): Chachamim enacted Kesuvas Benin Dichrin (that sons inherit their mother's Kesuvah) to encourage men to give property to their daughters, like to their sons.

55a: Stipulations of the Kesuvah are like the Kesuvah regarding Kesuvas Benin Dichrin.

(Chachamim of Pumbadisa): Kesuvas Benin Dichrin is not collected from land that was sold. The Mishnah says 'they will inherit.' (Heirs do not collect land that their father sold.)

(Chachamim of Masa Machsiya): It is collected from land that was sold. The Mishnah says 'they are owed.' (A creditor collects from sold land.)

The Halachah is, it is not collected.

90a (Mishnah): If a man married a woman and she died, then he married a second woman and he died, the second woman or her heirs collect before the heirs of the first wife.

90b: We learn from the Mishnah that Kesuvas Benin Dichrin is not collected from sold land;

If it were, the heirs of the first wife would collect from the heirs of the second.

91b (Mishnah): If a man married two women and died after them, and the orphans demand the Kesuvah of their mother and there is enough only to pay the Kesuvos, the heirs split the estate equally;

If there is a Dinar more than the Kesuvos, the sons of each mother receive their mother's Kesuvah. If orphans (of one mother) request to accept property at an inflated price, in order that the estate will be considered to have an extra Dinar, we do not accede. Rather, Beis Din evaluates the property.

Rishonim

Rif and Rosh (22a, and 5:1 b'Sof and 5:2): Stipulations of the Kesuvah (including Tosefes) are like the Kesuvah regarding Kesuvas Benin Dichrin. Each woman's sons receive her Kesuvah, including the Tosefes. The Halachah is, Kesuvas Benin Dichrin is not collected from land that was sold. The Mishnah says 'they will inherit.'

Rambam (Hilchos Ishus 19:1): It is a stipulation of the Kesuvah that sons inherit their mother's Kesuvah and dowry of Tzon Barzel. Afterwards they divide the rest of the inheritance equally with their brothers.

Rambam (3): This is when there was at least a Dinar above both of the Kesuvos, in order that they will split the rest equally. If not, they split everything equally. If the enactment would apply, it would Mevatel the equal division of brothers, which is mid'Oraisa.

Rambam (16:7): Ge'onim enacted that a woman can collect her Kesuvah from Metaltelim. The enactment spread through all of Yisrael. It applies to all stipulations of the Kesuvah, except for Kesuvas Benin Dichrin. Therefore, I say that Kesuvas Benin Dichrin is only from land.

Mordechai (162): Ba'al ha'Itur cites a Teshuvah in which R. Chanina b'Rebbi Yehudah says that we do not collect Kesuvas Benin Dichrin anymore because it must be from property that has Acharayos. We need an assessment of Beis Din and Zekenim that the property is worth both Kesuvos (and perhaps we are not qualified). Further, the purpose was so that men will give to daughters like to sons, and nowadays, (people give more to daughters,) if only one would give to his son like to his daughter! It is proper to excommunicate for giving too much to daughters. Mar bar Rav Huna says similarly. Therefore, also we do not collect. Tosfos says that we collect even from Metaltelim (nowadays), for stipulations of the Kesuvah are exactly like the Kesuvah.

Rosh (ibid.): Rashi says that if there was an extra Dinar, even if a creditor had a lien and collected it, Kesuvas Benin Dichrin applies. If there was not an extra Dinar, even if a creditor had a lien and later collected it, Kesuvas Benin Dichrin does not apply. This is because a creditor collects from now and onwards, so the heirs of the smaller Kesuvah already merited that the enactment does not apply. Some Gedolim say that Kesuvas Benin Dichrin applies only when they receive the entire Kesuvah of their mother. This is unreasonable. Since there was enough at the time of death, they already merited and do not lose it later.

Rosh (ibid.): Even though latter Chachamim enacted to collect a Kesuvah from Metaltelim, they did not enact this for Kesuvas Benin Dichrin.

Beis Yosef (DH Aval): The Rif did not say so. It seems that he holds that Chachamim argue with R. Shimon and hold that the enactment applies even to Metaltelim, even though a Kesuvah is collected only from land. And even if you will say that Chachamim also say that it is only from land, now that later Chachamim enacted to collect a Kesuvah from Metaltelim, Kesuvas Benin Dichrin applies to Metaltelim.

Poskim

Shulchan Aruch (EH 111:1): It is a stipulation of the Kesuvah that sons inherit their mother's Kesuvah and dowry of Tzon Barzel. Some say that Tosefes is included.

Question (Chelkas Mechokek 1): All agree that Tosefes is included. The Gemara explicitly says that Tosefes is like the Kesuvah regarding Kesuvas Benin Dichrin!

Shulchan Aruch (ibid.): Afterwards they divide the rest of the inheritance equally with their brothers. E.g. Yakov married Leah, and her Kesuvah and dowry (combined) were 1000, and she gave birth to Reuven and she died. Later, Yakov married Rachel. Her Kesuvah and dowry were 200; she gave birth to Yosef and she died. Yakov died later, leaving 2000. Reuven inherits his mother's Kesuvah of 1000, Yosef inherits his mother's Kesuvah of 200, and they divide the rest equally. In all, Reuven gets 1400 and Yosef gets 600.

Shulchan Aruch (2): This is when there was at least a Dinar above both of the Kesuvos, in order that they will split the rest equally. If not, they split everything equally. If the enactment would apply, it would Mevatel the equal division of brothers, which is mid'Oraisa.

Shulchan Aruch (13): Anyone who inherits the Kesuvah of his mother who died in his father's lifetime, does not take from sold property. He takes only from Bnei Chorin, like all heirs.

Shulchan Aruch (14): Some say that this is only from land, that Kesuvas Benin Dichrin applies only if there is enough land for both Kesuvos, but not if there was only Metaltelim. However, if there is enough land for both Kesuvos, even if the extra (Dinar) is only from Metaltelim, the enactment applies. Some say that nowadays that we write in the Kesuvah (a lien on) Metaltelim Agav (via) land, also Kesuvas Benin Dichrin is collected from Metaltelim, for stipulations of the Kesuvah are like the Kesuvah.

Beis Yosef (DH v'Af): Nowadays, we write in the Kesuvah a lien on Metaltelim Agav land for all stipulations of the Kesuvah. One might have thought that therefore also Kesuvas Benin Dichrin is collected from Metaltelim nowadays. However, the Rambam said that it is not collected because inheritance of Kesuvas Benin Dichrin did not spread throughout all the Yeshivos. Many Ge'onim say that it does not apply at all nowadays. Therefore, we left it according to the law of the Gemara. It seems that the Rosh agrees, for he says that it is collected only from land, without distinguishing whether or not a lien was put on Metaltelim Agav land. However, the Rivash (106) brings the Poskim, Rambam and Rosh, then says that nowadays that we write a lien on Metaltelim Agav land, letter of the law it is collected from Metaltelim, even without the Ge'onim's enactment (to collect from Metaltelim in every case).