Yevamos 5:2

(This mishna continues from the previous one, explaining the situation described there.) If a man married his brother’s widow with money or a document but did not consummate the marriage (this is called “maamar”), and he gave her a get, he must also perform chalitzah. If he married her by maamar and performed chalitzah, he must also give her a get. If he married her with maamar and then consummated the marriage, he has properly performed yibum.

Yevamos 5:3

If he gave her a get and then married her by maamar, he must give her another get and perform chalitzah. If he gave her a get and consummated the relationship, he must give her a get and perform chalitzah. If he gave her a get and performed chalitzah – that’s it; nothing follows chalitzah. If he performed chalitzah and then married her by maamar or gave her a get or consummated the relationship, or if he consummated the relationship and then married her by maamar, or if he gave her a get and performed chalitzah – whatever he did after chalitzah is of no legal impact. It makes no difference whether there is one widow and one brother or two widows and one brother.