Automating Subitems using Line Items

We import our contacts weekly and need to be able to import then trigger some of the columns from the line item to move into columns in a subitem. Our example is we have clients who have gone through a bereavement - we need the bereaved to be a subitem as this person may have more bereavements which will need to be added as additional subitems. As we get 100’s a week we would love this to be able to be automated.