Look in your transaction history on the IRA. Every last day of the month, you should see a dividend payment (that’s your interest) and a reinvestment of the same amount (putting the interest into VMFXX).

I think the shared checking account is probably the best option. If you want a way to spend money from that account with credit card rewards, one of you could get a credit card (or designate one you already have), make the other person an authorized user, and only pay for shared expenses on that card. Then, pay that card only from your shared checking account.

I would warn you against trying to time the market. If you view that money as long term then the best plan is an index fund/ETF regardless of what the fed is doing right now. You have no idea when the market will shift. If you need the money safe in CDs, that should be the plan going forward as well.