手紙 is the direct object. 家 is the place it was sent to, so I suppose that counts as an indirect object. Sentence order for Japanese is very flexible (although the verb must always come last), so I wouldn’t worry too much about memorizing any particular order beyond Subject-Object-Verb.
Edit: I took a look at the source you gave, and I think you should probably disregard this sentence pattern. It’s clear from the purpose of the lesson that they were purposefully trying to shoehorn から, へ, and に into single sentence. I don’t think it sounds particularly natural.
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