Since your husband didn't have any vested financial interest in the home he wouldn't receive a 1099 for the home sale. The money received from his step siblings is considered a gift. Gift treatment is a bit different. The person(s) who gave the gift files the gift tax return, if necessary, and pays any tax. Essentially, gifts are neither taxable nor deductible on your tax return. The annual exclusion for gifts is $15,000 for 2020.
Here's a great article on The Gift Tax https://turbotax.intuit.com/tax-tips/estates/the-gift-tax/L1sFpFeXV
