"We have to write."

[BwanaSimba]

This should then be: 'tuandike'.

[AGreatUserName]

Nah, that's more like "let's write" or "we should write". (All the parts in this course where the subjunctive on its own is translated with "have to" are a bit dodgy.) "We have to" would either be something like Lazima tuandike or Tunahitaji kuandika.