You and your spouse are seen as one taxpayer by the IRS and even if multiple plans were setup, the IRS would require they all be treated as one plan.

It is possible to keep two separate bank accounts, if your spouse chooses to keep her funds separate. Remember your Solo 401k is not the bank account. Your Solo 401k is a plan and a trust and the bank accounts are just the places where you manage the assets of the plan.
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