My question doesn't really matter in your case, actually. I made assumption, as I usually do on this forum, that you're under 59.5, but since that's not the case you can access retirement accounts at any time, so it really doesn't matter if you have 5 years of expenses or not.
Honestly, given your husband's situation and that putting the money in Roth is making you anxious -- just don't. It's not the end of world either way.
If you still want to think about this -- remember that Roth contributions can always be withdrawn, so you're really not locking them up any more than you are otherwise. In fact, withdrawing contributions from Roth would have no implications, while withdrawing invested money from a taxable account would incur capital gains, so in some ways money in Roth is even more flexible.
There is one 5 year thing that comes in to play. Have you had a Roth account open for at least 5 years? If so, and since you're over 59.5 you can withdraw anything (contributions or gains) from Roth at any time without restriction, so it's the ultimate flexible account.
From some of your question is the OP I'm wondering if you're conflating contributing to Roth and investing? Those are independent questions. You can even open a Roth IRA and Ally bank (probably others) and leave the money in a savings account or open a CD and not pay tax on the interest.