I don't know the answer to this, but I'll address what I do know below.
If he were still employed under OPT and they were applying now, and his employer could provide a letter that they'd continue to employ him, it would work out. Since his OPT for expired a year ago, and he has no legal income now and hadn't for a year, it doesn't mean much.
Your husband will file a separate I864, including himself, yourself, and your friend's husband as the "household", unless you also have children or other dependents.
You may choose to also submit I864a. You don't technically have to, if your husband alone can carry the sponsorship requirement. However, if you file taxes married jointly, since the IRS transcript doesn't actually specify who earned what, people usually do it just to make it easier. If you don't, he'll have to submit W2s and pay stubs to specify his part of the income.
Do you mean that your friend and her husband live with you?
If so, I'm actually not certain whether your husband (and/or you) can submit I864a. You live together, but you're not a family per se. Maybe?
I believe you always have the option to submit a totally separate affidavit (I864), regardless of familial or residential engagements.
I want to just use separate big paper clips for each type of evidence and instead of exhibit A, B, C etc. just do tabs with short description of what type of evidence it is and put on top of each part of submission.
For example:
1) Tax Transcripts and Tax Returns 2015 - 2017
2) Statements from joint Chase Bank account 2016-2018
3) Statements from joint Citi Bank account for 2017-2018, checks and deposits to/from this account
4) Electricity utility bills showing both our names 2016-2018
5) Cable utility bills showing both our names 2016-2018
6) Lease agreements showing us both as tenants 2016-2019
7) Various pictures of us together 2015-2018
Something like that... I saw beautifully organised submissions on VJ, where people use ACCO fasterners but it seems too complicated, need to also get a hole puncher and punch all these holes...
So I guess the main point is to submit everything organized and easy to access for an officer
