Yevamos 5:4

(Continuing from the previous mishna.) If the surviving brother married two widows with maamar, he must give each a get and perform chalitzah with one of them. If he performed maamar with one and gave the other a get, the former requires a get and one of them requires chalitzah. If he performed maamar with one and consummated the relationship with the other, each one requires a get and one of them requires chalitzah. If he married one with maamar and performed chalitzah with the other, the former requires a get. If he gave each one a get, one of them requires chalitzah. If he gave one a get and consummated the relationship with the other, the latter requires a get and one of them requires chalitzah. If he gave one a get and married the other with maamar, the latter requires a get and one of them requires chalitzah. If he gave one a get and performed chalitzah with the other – that’s it; nothing follows chalitzah.

Yevamos 5:5

If he performed chalitzah with each of the widows, or if he performed chalitzah with one and maamar with the other, or gave the second a get, or consummated the relationship; or if he consummated the relationship with each, or he consummated the relationship with one and performed maamar with the second, or gave her a get, or performed chalitzah with her – in all of these cases, whatever he does after chalitzah has no legal effect, whether there is one widow and one brother or one widow and two brothers.