To override the minSDK use:

<uses-sdk tools:overrideLibrary="com.xxxx.xxxx"/>

To fix the merge error use:

android {
packagingOptions {
    pickFirst 'google/protobuf/*.proto'
    pickFirst 'google/protobuf/compiler/*.proto'
    }
}

source: https://github.com/protocolbuffers/protobuf/issues/8694