Order of searchable attibutes

Hi,
I am trying implement a search page in following page and wondering what is the right way to implement some of these functionalities.

demo page: Soil Health Knowledgebase
Using JS instantSearch

My issues are implementing Order By and Search Within functionalities.
In Search within, for example user should be able to search in author attribute.

  • Do I have to create separate indices for each of these?
    e.g soilhelath_title_asc, soilhelath_date_desc
  • Can I do this with virtual replicas?
    sortBy({
        container: '#sort-by',
        items: [
            { label: 'Most relevant', value: 'DEV_SHKB' },
            { label: 'Title (asc)', value: 'title_asc' },
            { label: 'Published date (desc)', value: 'published_date_desc' },
        ],
    }),

    sortBy({
        container: '#search-in',
        items: [
            { label: 'Entire page', value: 'DEV_SHKB' },
            { label: 'Author (asc)', value: 'DEV_SHKB_in_author' },
        ],
    }),

Thanks
Sudeera