Which form would be the correct for reflexive verb lavarse subject ellos?

The correct form for the reflexive verb *lavarse* with the subject *ellos* is se lavan.

Here's why:

* Reflexive verbs are verbs that reflect the action back on the subject. They always use a reflexive pronoun (me, te, se, nos, os, se).

* Lavarse means "to wash oneself".

* Ellos is the third-person plural subject (they).

* In the present tense, the third-person plural form of *lavarse* is se lavan.

So, the complete sentence would be: Ellos se lavan. (They wash themselves.)