What happens to the balance of an RA fund upon death?

This depends on the type of pension (annuity) your husband bought.

Conventional annuity: if he bought one with a so-called spousal benefit, then this would continue to pay out after his death, albeit at a reduced rate, for as long as the spouse survives. But if it is an annuity for a single person, then this will cease on his death (and only on his death). He would continue to receive the latter pension even if the wife passed away first. The capital dies with the member/surviving spouse and no benefit remains for any siblings.

Living annuity: the capital does not die with your spouse; you effectively take over what is left of the living annuity. Your nominated beneficiaries will take over what is left after your passing.