Swift Package Manager Library with multiple files

I have and Swift Package Manager Executable project that also includes a library. Inside that library I want to have multiple files that all combine into one library.

Package.swift

// swift-tools-version:5.0
// The swift-tools-version declares the minimum version of Swift required to build this package.

import PackageDescription

let package = Package(
    name: "sandbox",
    products: [
        .library(name: "library", targets: ["library"]),
        .executable(name: "sandbox", targets: ["sandbox"]),
    ],
    dependencies: [
        // Dependencies declare other packages that this package depends on.
        // .package(url: /* package url */, from: "1.0.0"),
        .package(url: "https://github.com/apple/swift-package-manager.git", from: "0.4.0"),
        .package(url: "https://github.com/scinfu/SwiftSoup.git", from: "2.2.0"),
    ],
    targets: [
        // Targets are the basic building blocks of a package. A target can define a module or a test suite.
        // Targets can depend on other targets in this package, and on products in packages which this package depends on.
        .target(
            name: "library",
            dependencies: ["SwiftSoup",]),
        .target(
            name: "sandbox",
            dependencies: ["library", "SPMUtility"]),
        .testTarget(
            name: "sandboxTests",
            dependencies: ["sandbox"]),
    ]
)

File Structure

Sources
    --sandbox
      |--main.swift
    --library
      |--library.swift
      |--class1.swift
      |--class2.swift

I can call methods from the library.swift in main.swift but I cant call methods from class1.swift and class2.swift in main.swift.

What do I have to do to get this working properly? I would like to keep the files split up for organization purposes instead of putting all the code inside library.swift.