"Jak často si píšete?"

Translation: How often do you write to each other?

[zubkov318]

Why "naše rodiny se nenavidí" (if I remember right other task), but "často si píšete"?

[ion1122]

Some verbs take the se form, others take the si form of the reflexive. The si form is dative.

Compare, for example:
"Jak často si píšete dopisy?"

(Please correct my sentence above if it is wrong.)

[FrancorSZL]

I wrote: How often are you writing to each other. Why is not this solution correct?

[VladaFu]

For habitual action English uses the present simple tense.

[Werner_Rietveld]

Is the 'to' in 'write to each other' necesary?

[VladaFu]

It is accepted without.