Morphologically them + -selves.

• IPA: /ðɛmˈsɛlvz/, /ðəmˈsɛlvz/

1. (reflexive pronoun) The reflexive case of they, the third-person plural personal pronoun. The group of people, animals or objects previously mentioned, as the object of a verb or following a preposition (also used for emphasis).

   (reflexively): They’ve hurt themselves.

   (after a preposition): They fought among themselves.

   (for emphasis): They are going to try climbing Mount Everest themselves.

   • 1918, W[illiam] B[abington] Maxwell, chapter XVI, in The Mirror and the Lamp, Indianapolis, Ind.: The Bobbs-Merrill Company, →OCLC ↗:

     The preposterous altruism too! […] Resist not evil. It is an insane immolation of self—as bad intrinsically as fakirs stabbing themselves or anchorites warping their spines in caves scarcely large enough for a fair-sized dog.

2. (reflexive pronoun) The reflexive case of they, the third-person singular personal pronoun. The single person previously mentioned, as the object of a verb or following a preposition (also used for emphasis).

   (reflexively): Would whoever stole my phone please make themselves known.

   (after a preposition): I don't want anyone to fight among themselves.

   (for emphasis): Everyone must do it themselves.

   • 1611, The Holy Bible, […] (King James Version), London: […] Robert Barker, […], →OCLC ↗, Philippians 2:3 ↗:

     Let nothing be done through strife or vainglory; but in lowliness of mind let each esteem other better than themselves.

• 'emselves (colloquial)
• theirselves (nonstandard)
• (singular) themself (non-gender-specific), theirself (non-gender-specific, but nonstandard), himself, herself (gender-specific)

• French: se
• German: sich
• Portuguese: se, si (prepositional)
• Russian: себя́
• Spanish: se

• French: eux-mêmes, elles-mêmes
• Portuguese: eles mesmos, elas mesmas
• Russian: они́ сам
• Spanish: ellos mismos, ellas mismas

• Russian: себя́