If you/husband decide to sign, arrange for the payment notices to come to you. If not, the relative could be in default for months before you, as the co-signer, are notified.
Also, find out what the deal is with consolidating loans with different co-signers. If they can’t be consolidated, the student might be able to consolidate all other loans and yours is left out. The relative may make the other payments and yours is paid last, or never.
It’s pretty risky.