отсортировать?
foreach ($terminal_list as $district) {
$district_name = $district["name"];
$district_terminals = $district["terminals"];
foreach ($district_terminals as $terminal) {
$name = $terminal['name'];
$address = $terminal['address'];
$data = json_decode(getCoords($address),true);
$position = $data["response"]["GeoObjectCollection"]["featureMember"][0]['GeoObject']["Point"]["pos"];
$terminal["position"] = $position;
}
var_dump($district_terminals);
}