In California, a child can be moved to another county with the agreement of both parents, but a child cannot be moved out of state (or obviously out of the country) without a court order.
As long as there is joint legal custody, then yes, Ioan has legal say so on where they live. If Alice were to move with the children anywhere out of California, without the court’s consent, that could be seen as parental kidnapping.
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He can’t dictate the exact location. Legally, Alice just needs to live in LA county, unless they both agree she can move to, say, nearby Orange or Ventura County. It’s not hard to get permission to move to another county, btw, if you can show just cause (cheaper housing, job relocation, etc.).
It gets more complicated if you move further away and impede visitation. If Ioan actually had visitation and Alice moved to, let’s say, Las Vegas, she would need to arrange and pay for the children to fly back to LA for regularly scheduled visits, or pay for Ioan to come to Vegas.