Answer by Oleksandr Berehovskyi for How can I change the output display in lightning app of sales force other than table?

you can use lightning-layout and lightning-layout-item with specifying size of each layout-item on the parent component, where those 3 datatables should be rendered.

<template><lightning-card><lightning-layout multiple-rows><lightning-layout-item size="6"><c-datatable1></c-datatable1></lightning-layout-item><lightning-layout-item size="6"><c-datatable2></c-datatable2></lightning-layout-item><lightning-layout-item size="6"><c-datatable3></c-datatable3></lightning-layout-item></lightning-layout></lightning-card></template>