Where does “those're” come from?

those're (English) comes from English ’re, from English are, from Middle English aren, from Old English earon, from Old English bēon, from Proto-Germanic bijōniz, from Proto-Germanic bijǭ, from Proto-Indo-European bʰey- — bee.

Ancestry of “those're”, step by step

those're traces back through two separate lines of ancestry.

via English ’re

StepLanguageWordMeaning
1English’reinflection of the verb "to be"
2Englisharesecond-person singular simple present of be;...
3Middle EnglisharenPlural present indicative form of been
4Old Englishearonthird-person plural simple present of wesan
5Old Englishbēonto be, become
6Proto-Germanicbijōniz
7Proto-Germanicbijǭbee
8Proto-Indo-Europeanbʰey-bee

via English those

StepLanguageWordMeaning
1Englishthoseplural of that
2Middle Englishthosthose
3Middle Englishthothe
4Old Englishþāthe, those; then, when; those
5Proto-Germanicþaithey; those; nominative plural masculine of *sa
6Proto-Indo-Europeanto-it; that; the, that
7Proto-Indo-Europeanthis; that
Every word from Proto-Indo-European bʰey-