ESIGN is never a primary concern. It simply gives you permission to substitute electrons for paper--but the all-important issue is what is printed on the paper. If the paper contains federal disclosures and the laws/regs that require these disclosures mandate that they must be delivered to the consumer "in writing", then you must use paper OR ESIGN-enabled electronic documents.
Assuming the account opening process includes delivery of contract documents, you would be wise to consult with local counsel. If they are involved in litigation, contract documents will be judged under state law. Many of the states have enacted some form of the UETA. If your electronic contract documents do not conform with this state law, a judge could throw them out as unenforceable.
I assume that "the joint" means joint account holders and not a prison. The same regs that tell you what to disclose (and when) will also tell you to whom the disclosure(s) must be delivered. If all parties must be given a separate set of the disclosures in question, then you will need consent from each party before substituting electrons for paper.
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...gone fishing.