My husband has gone overseas. I have power of attorney. Can I pick up his son during his weekends. My husband would like to see him when we video chat

The unwritten subtext of your question is that the custodial mother is uncooperative.  Is that the case? Before you lawyer up on this and start talking about what rights you have under the power of attorney, doesn't it make a lot more sense to propose the idea to the custodial mother. Any court that looks at this issue will act in the best interests of the child, and it seems reasonable to assume that it is in the best interests of the child to maintain contact with his father. Your husband has visitation rights, so there should be no issue with virtual visitation. Still, the first thing a court or other mediator will ask is why the father and mother didn't just sort this out between themselves without involving the legal system. Visitation rights are personal to a specific individual, so you can't act in place of your husband.  The power of attorney doesn't make you him for visitation purposes.