the selling expenses I can just group under the main house I assume I don’t have to allocate to each one
You can allocate if you want. But overall, you're correct. So long as you still show a gain after subtracting the selling expenses from the selling price, you'll be fine.
I'll usually allocate my selling expenses between the structure and the land. So if I have a selling price for the property that is 70% structure and 30% land, I'll allocate the selling expenses similarly. I'll make slight changes if necessary so I don't end up showing a gain on the structure and a loss on the land.
Since I've accounted for all my selling expenses to be deducted, on the main property asset, I don't bother allocating them to other assets unless I really need to.
