We have an interesting debate between Rashi and the TT. [Yes, one MAY argue with Rashi and still be a Kosher Yid!] :-)
Rashi posits that any children Yoseph WILL have after Ephraim uM'nashe will be subsumed under THEIR names...
The Torah Temimah 48:5:5 objects because "Holadta" is PAST tense.
Rather TT suggests that this refers not to the future siblings of Ephraim and M'nasheh, but towards their respective children, some of which may have already been born.
Tangentially one may understand the quoted G'mara as quoting Passuq 5 as its source text as also referring to Passuq 6