"His wife is coming home tomorrow morning."
Translation:Hans fru kommer hem i morgon bitti.
There are two kinds of kommer, one is the future construction kommer att which is a lot like 'is going to' in English. Here, you can skip att in spoken or informal language.
The kommer in this sentence really means comes. This is not a modal or auxiliary verb. You can't have an att after this one.
is coming home is present tense in English, even though it can sometimes have a futural meaning like here. However, in Swedish it is much more common to use the present tense with a futural meaning than it is in English. Therefore it doesn't make much sense to translate an English sentence with present-for-future into a Swedish sentence in the future tense.
The other way around though is often a good idea.
So Hans fru kommer att komma hem should be His wife will come home or …is going to come home in English.
Your sentence is ungrammatical because the verb absolutely has to go in second place in main clauses. You can rearrange other stuff, but kommer must be in second place.
I morgon bitti kommer hans fru hem.
Hans fru kommer hem i morgon bitti.
?Hem kommer hans fru i morgon bitti (this sentence is grammatically correct but not an accepted answer here because it's so special that you'd need to add some specific context for it to work).
One 'place' in this sense is a sentence constituent, it can be much longer than one word but it's something that could in principle be replaced with one word. Longer post about word order here: https://www.duolingo.com/comment/8970470