Commentary for Yevamot 5:5

חלץ וחלץ – he is permitted [to be married to] the relatives of the second [woman] for there is nothing after the first Halitzah any levirate connections, and Halitzah with both is nothing, for even to the priesthood, she is not invalidated. And similarly, if he performed Halitzah with the first [widow of the deceased childless brother] and made a statement [of intention of levirate marriage] with the second [widow], and similarly, if he had given a Jewish bill of divorce to this [second] one after performing Halitzah with that one, or performed an act of coition with this one after the Halitzah of that one, the act with the latter person is not worthless. [Or] if he performed an act of coition with this one first and then returned and performed an act of coition with the second, or performed an act of coition first and then made a statement [of intention of levirate marriage] with the second , or gave a Jewish bill of divorce to the second, or performed Halitzah with the second, there is nothing after an act of coition at all, and the final act is not considered, and he is permitted with the second’s [female] relatives.

If he performed halitzah [for one] and then performed halitzah [for the other],
Or performed halitzah [for one] and did ma'amar [with the other], or gave her get, or had intercourse with her;
Or if he had intercourse [with one] and then with the other,
Or had intercourse [with one] and then ma'amar with the other, or gave her a get, or performed halitzah there is nothing after halitzah.
[There is no difference in the law] whether there was one yavam to two yevamoth or two yavamim to yevamah.
This mishnah continues to teach that once one of the yavamim has performed halitzah or yibbum with one of the yevamoth, any subsequent action done with the other yevamah, be it halitzah, a get, ma’amar or intercourse, is meaningless.
Section one: In this case the yavam has halitzah with one of the yevamoth and then halitzah with the other. As we will learn in section four, since the second halitzah was unnecessary, it has no effect. He can marry that halutzah’s relatives and she can marry his.
Section two: Similarly, if he has halitzah with one and then ma’amar, a get or intercourse with the other, the subsequent actions are invalid. The woman who received ma’amar does not need a get, nor does the woman with whom he had intercourse. The woman who received the get is not a divorcee but a widow, who may subsequently marry a kohen. In all of these cases, he can marry her relatives and she may marry his.
Sections three and four: These sections teach the same ruling, but with regard to yibbum, performed through intercourse. Once the yavam has yibbum with one of the yevamoth, all subsequent actions are invalid. Although the mishnah states only that “there is nothing after halitzah”, the meaning is that there is nothing after halitzah or yibbum, as was taught in mishnah one of our chapter.
Section five: The rule that there is nothing after halitzah (or yibbum) is true whether or not there was one yavam who had halitzah with one of two yevamoth (and then did something else with the other yevamah), or two yevamim, one of whom had halitzah or yibbum first with one yevamah (and then the other brother did something else with the same yevamah). In all cases, once one brother has had halitzah or yibbum with one yevamah, all subsequent actions are meaningless.

אין אחר חליצה כלום – It is referring to the first clause [of the Mishnah], but regarding the concluding clause, it is necessary to state that there is nothing after an act of coition.