From what I know.......
Unless Chris co-signed to any of Barb's loans (a reasonable possibility, since she has borrowed off of his life insurance), he'd be on the hook for that.
However, since he's 100% on the Tugboat, the worst they could do is to cancel the LI policy and report the debt to a collection agency since his TB money is exempt from collection. This means that Chris won't get his SSI garnished, but it will result in other bad things, such as his credit card companies revoking his cards and giving him a poor credit score which will prevent him from getting an apartment on his own.
As for any increase in the Tugboat money, if he's getting $1000+ each month, then that means he's already getting half of what Bob took in added to his check as a "Survivor". He won't get any more money added on after Barb's dead.
DR;TL version: Barb dies, Chris get a ton of her debts because he co-signed, companies can't collect so they'll just dump the debt onto a collection agency who will never get anywhere because Chris never answers the phone, Chris' credit score goes into the toilet, credit cards are revoked, Chris cannot find a new place because all the landlords say he has too bad a credit score. Chris and Phil fight over a roasted rat behind the 7-11.
I think I saw from an ancient thread, that she's going to have her carcass put into the same crypt that Bob is in. So chances are Bob may have done something to include her in a burial contract. No sign of anything prepared for Chris though, so it looks like he'll just be left out on the curb on trash day on the week he expires.
Well, maybe then those vouchers will finally come in handy.