A 3MS placeholder for a compound subject is often followed by a 3MP placeholder for the same compound subject, e.g., Gen 9:23, וַיִּקַּח שֵׁם וָיֶפֶת אֶת הַשִּׂמְלָה וַיָּשִׂימוּ עַל שְׁכֶם שְׁנֵיהֶם וַיֵּלְכוּ אֲחֹרַנִּית וַיְכַסּוּ .
This also occurs with a 3FS followed by 3FP placeholder, e.g., Gen 24:61, וַתָּקָם רִבְקָה וְנַעֲרֹתֶיהָ וַתִּרְכַּבְנָה עַל הַגְּמַלִּים וַתֵּלַכְנָה אַחֲרֵי הָאִיש , and a 2MS followed by a 2MP placeholder, e.g., Exod. 3:18, וּבָאתָ אַתָּה וְזִקְנֵי יִשְׂרָאֵל אֶל מֶלֶךְ מִצְרַיִם וַאֲמַרְתֶּם אֵלָיו
On the other hand, Gen. 14:15 appears to have the 3MS placeholder for a compound subject followed by the same 3MS placeholder for it - וַיֵּחָלֵק עֲלֵיהֶם לַיְלָה הוּא וַעֲבָדָיו וַיַּכֵּם וַיִּרְדְּפֵם (I know you could argue otherwise).
Why would a singular placeholder for an overt compound subject immediately switch to a plural one in the next clause? Is the singular placeholder for the first subject only, and then it is compounded? Or, is it partly style? Or, partly semantics, e.g., the first noun is the head of a group or entity or collection? Or, is it a combination of any of these?