no, you cant. You need the long-lost relative papers (I'm not sure if that is what it is called), and you just have to click on them and choose what relation you have to them. An alternate way is to get the villager editor from creative and go to the family tree. You then type: add me mother OR add me father To be the parent of the child/villager.
Source: Past experience :)
Pages in category "Can you make a MCA villager become your child if the parents are deceased"
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