For any retirement/trading account, there can be only one owner, and I've not seen an account that wouldn't allow a named beneficiary (not that means that there isn't one, but I have a taxable investment account, 401k, traditional IRA, rollover IRA and a Roth and all allow beneficiaries).
To check the beneficiary arrangement on the FID account, all he needs to do is log in, go to Accounts & Trade, then Update Accounts/Features (towards the bottom of the list), then Account Access Rights (Power of Attorney and Trading Authorization), and then Beneficiary Information. This will pull up who is the beneficiary (if any) and should give him the option to either update online or instructions on how to do so. If there is no designation, then the account(s) would fall into the area of probate, meaning that they'd eventually pass to you once the estate was settled, but if there is a beneficiary or transfer on death designation, then you get possession within a week or two at most after sending in the paperwork and a death certificate.
I have my retirement accounts (401k, Roth, traditional IRA) set up with the husband as the sole beneficiary, but the taxable account is also designated "TOD" for transfer on death after the account number, in addition to having him as the beneficiary. That also means that none of these accounts will go through probate.
And from what I sort of understand, if you're not on the house deed, but still his sole beneficiary, then the house would eventually come to you (and i can't imagine there being any issues with you continuing to live there during probate), but it would have to go through probate and would be counted as part of his estate (same thing for any accounts you're not already named as a beneficiary). This is what happened when my dad died, and honestly, it was easy with the stuff that was already set up with beneficiaries... took almost a year to get possession of the non-beneficiary accounts.