California taxes a nonresident on income earned while physically present in the state. From your post, it appears your husband's income would not be taxed to California because he performs all the work in Idaho.
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The property sale is California source income because the property is in California.
The stock would depend on the type. If it's regular publicly traded stock, then it is not California source income. If it is employee stock or stock in a private California corporation then it may be California income.
The 401(k) contribution would be Idaho, assuming, as mentioned above, that all the work was done from home in ID.
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