The IRS is going to consider both Solo401ks to be one plan, since you are spouses and considered related in the eyes of the IRS. This is the concept of “Controlled Group” in the US tax system.
If you have two entities of any kind, and you own both of them, then they are both one in the eyes of the IRS. The IRS views a married couple as one tax payer (hence, filing jointly). You and your spouse are the same person for tax purposes, and if you have one corporation and your spouse has another, the IRS will consider it to be one corporation. Thusly, if you and your spouse have two retirement accounts, the government can require that you treat it as one. For further questions, please consult your CPA or tax advisor.