TT #744 · Parashas Ki Seitzei · Seventh Aliyah · Passuk 25:09
Then his yevamah shall approach him in the presence of the elders, and draw his shoe off his foot, and spit in his face, and respond and say: “Thus shall be done to the man who will not build up his brother’s house.”
Torah Temimah points to Yevamot 10b / 24a.
TT lemma: בֵּית אָחִיו.
בֵּית אָחִיו – בַּיִת אֶחָד הוּא בּוֹנֶה, וְאֵינוֹ בּוֹנֶה שְׁנֵי בָּתִּים.
English: “His brother’s house” — he builds one house and does not build two houses.
On the daf / in context: The language is used to exclude taking both the yevamah and her co-wife.
Derash limiting the yavam to one house.
The yavam may take only one of the widows; he may not perform yibbum with two co-wives.