Indexing and filtering in Elasticssearch using the NEST (HighLevelClient) without using POCO objects

Question

I'm using the ElasticHighLevelClient (NEST) to index data from SQL DB storage. The problem is that I don't have access to the POCO objects and that I have to filter over this data. POCO objects have nested fields, for example

class Car{
public string Id { get; set; }
public string Name { get; set; }
public string Model { get; set; }
public List<Engine> Engines { get; set; }
public List<Wheel> Wheels {get; set;}
}


class Engine {
public string Id { get; set; }
public string EngineModel { get; set; }
public TypeEnum Type { get; set; }
public List<Maker> Makers { get; set; }
}

class Wheel {
public string Id { get; set; }
public string Name { get; set; }
} 

class Maker {
public string Id { get; set; }
public string CompanyName { get; set; }
}

I found this question Bulk Indexing in Elasticssearch using the ElasticLowLevelClient client but i have several problems with it: 'PostData.PostData(string) is inaccessible due to its protection level. I changed it to new PostData.Serializable(stringJson)); but i've got "cannot resolve symbol 'Serializible'" error.

So, can anybody help me with next moments:

1) How can I index Car object without having access to the POCO objects?

2) How can I setup filtering with nested objects for example all cars that have an Engine.Type = “petrol” and Engine.Maker = “ltd”?

Thanks!