我尝试将我的JSON数据转换为特定的ArrayList

我的示例JSON文件

$personData = @'
{
  "persons": [{
      "johndoe": [{
          "id": "4334234 <>",
         
          "family_adress": {
            "mother": "address of family",
            "father": "",
            "brother": "address of family"
          },
          
          "childiren": {
            "first": 1024,
            "second":128
          },

          "years_activity": {
              "2021":  [ "sample entry-1", "sample entry-2" ],
              "2022":  [ "sample entry-1", "sample entry-2" ]
          }
     }],

      "johndoe2": [{
          "id": "4334234 <>",
         
          "family_adress": {
            "mother": "address of family...",
            "father": "",
            "brother": "...address of family"
          },
          
          "childiren": {
            "first": 25,
            "second": 12
          },

          "years_activity": {
              "2021":  [ "sample entry-4", "sample entry-r" ],
              "2022":  [ "sample entry-5", "sample entry-s" ]
          }
     }]

  }]
}
'@

我的函数捕捉第一个入口

function Get-FirstPropertyValue($obj, $propName) {
  $propNames = $obj.psobject.properties.Name
  if ($propName -in $propNames) {
    $obj.$propName
  } 
  else {
    foreach ($iterPropName in $propNames) {
        if ($null -ne ($val = Get-FirstPropertyValue $obj.$iterPropName $propName) ) {
          return $val
        }
      }
  }
}

$data = $personData | ConvertFrom-Json
$person = Get-FirstPropertyValue $data 'persons'
$propName = @($person.psobject.properties.Name)[0]

write-Host $propName
@($person.psobject.properties.Name)[0].Keys       # Nothing

Q：如何只访问嵌套的对象名？

My Expected Output:
------------------
family_adress
childiren
years_activity

我想访问，person > johndoe > subkeys ->（如果subkeys没有多个属性，则捕获其唯一的名称，因为我想将它们添加到数组列表中）