How to embed multiple Salesforce Lightning Web Components using lightning layout?

Hi Piyush,

You have to mention the size on the layout item. When you don't mention size on layout-item, it will become flexible in terms of width and each item occupy width according to its content. Total horizontal size is divided into 12 parts.

For Example

Size should be 6 for 50:50.

<div class="c-container">
    <lightning-layout horizontal-align="spread" multiple-rows>
        <lightning-layout-item padding="around-small" size="6">
            (My 1st LWC)
        </lightning-layout-item>
        <lightning-layout-item padding="around-small" size="6">
            (My 2nd LWC)
        </lightning-layout-item>
    </lightning-layout>
</div>

for more detail, you can refer https://lightningdesignsystem.com/utilities/grid/