@anjitaitsolutions Order page has the split order option in the dropdown if the following conditions met.
A) This order has multiple items in it or at least quantity more than one
B) This order has not been splitted yet, in case you want to split any order again so you need to remove a meta key from custom fields “split_status”, delete that and then refresh the page. You will see the split option again.
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About email on new order, shipping and billing details related issue is not actually related to this plugin as it is simply triggering the same email which WooCommerce sends. But I will check it again for you and will respond to the same support thread here.