struct Loaner: Codable {
    let loan_amt: String
    let firstname: String
    let combine_sc_details: Details

    struct Details: Codable {
        let dp_sc: Int
        let ltv_sc: Int
        let roi_sc: Float
        let vwBand: String
        //...
    }

    init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        self.loan_amt = try container.decode(String.self, forKey: .loan_amt)
        self.firstname = try container.decode(String.self, forKey: .firstname)
        let detailsStrings = try container.decode(String.self, forKey: .combine_sc_details)
        let detailsData = detailsStrings.data(using: .utf8)!
        self.combine_sc_details = try JSONDecoder().decode(Details.self, from: detailsData)
    }

}

let jsonStr = """
[{"loan_amt":"729442","combine_sc_details":"{\\"dp_sc\\": 560000, \\"ltv_sc\\": 315000, \\"roi_sc\\": 15.53, \\"vwBand\\": \\"-\\", \\"vwScore\\": 0, \\"dp_per_sc\\": 64, \\"tenure_sc\\": \\"60\\", \\"veh_offer\\": \\"no offer\\", \\"kuwy_score\\": \\"-1\\", \\"ltv_per_sc\\": 36, \\"loanProduct\\": \\"LP2\\", \\"multi_score\\": \\"-1\\", \\"decision_str\\": \\"SUBJECT TO DETALIED REVIEW\\", \\"product_band\\": \\"-\\", \\"experianScore\\": 0, \\"score_band_str\\": \\"S9\\", \\"subventionType\\": 0, \\"combined_score_int\\": \\"675\\"}","firstname":"HARIPRASANTH"},{"loan_amt":"729442","combine_sc_details":"{\\"dp_sc\\": 715000, \\"ltv_sc\\": 160000, \\"roi_sc\\": 15.53, \\"vwBand\\": \\"-\\", \\"vwScore\\": 0, \\"dp_per_sc\\": 81.71428571428572, \\"tenure_sc\\": \\"60\\", \\"veh_offer\\": \\"no offer\\", \\"kuwy_score\\": \\"-1\\", \\"ltv_per_sc\\": 18.285714285714285, \\"loanProduct\\": \\"LP2\\", \\"multi_score\\": \\"-1\\", \\"decision_str\\": \\"SUBJECT TO DETALIED REVIEW\\", \\"product_band\\": \\"-\\", \\"experianScore\\": 0, \\"score_band_str\\": \\"S9\\", \\"subventionType\\": 0, \\"combined_score_int\\": \\"675\\"}","firstname":"Naveen kumar"},{"loan_amt":"207954","combine_sc_details":"{\\"emi\\": 7308, \\"dp_sc\\": 31046, \\"ltv_sc\\": 249545, \\"roi_sc\\": 17.83, \\"vwBand\\": \\"-\\", \\"vwScore\\": 0, \\"raccRate\\": 17.83, \\"dp_per_sc\\": 12.989958158995815, \\"tenure_sc\\": 48, \\"veh_offer\\": \\"NO OFFER\\", \\"kuwy_score\\": \\"-1\\", \\"ltv_per_sc\\": 100, \\"loanProduct\\": \\"LP2\\", \\"multi_score\\": \\"-1\\", \\"decision_str\\": \\"SUBJECT TO DETALIED REVIEW\\", \\"exshow_price\\": \\"249545\\", \\"product_band\\": \\"-\\", \\"experianScore\\": 0, \\"roiSubvention\\": 0, \\"vehi_discount\\": \\"\\", \\"score_band_str\\": \\"S8\\", \\"sub_ven_Column\\": \\"STANDARD LOAN PRODUCTS\\", \\"subventionType\\": 1, \\"combined_score_int\\": \\"700\\"}","firstname":"KARTHIK"}]
"""

let jsonData = jsonStr.data(using: .utf8)!

do {
    let loaners = try JSONDecoder().decode([Loaner].self, from: jsonData)
    print(loaners)

    let sortedByName = loaners.sorted(by: { $0.firstname < $1.firstname })
    sortedByName.forEach { print($0.firstname) }

    let sortedByltv_sc = loaners.sorted(by: { $0.combine_sc_details.ltv_sc < $1.combine_sc_details.ltv_sc })
    sortedByltv_sc.forEach { print($0.firstname) }
} catch {
    print("Error: \(error)")
}