Hello and thanks for using Just Answer.
My name is ***** ***** am happy to assist you with your enquiry.
On the basis that no rent is being paid, you are correct in that your Son and his family have merely a Licence to occupy, as opposed to a Tenancy.
Therefore, to end the oral agreement you have, you are within your rights to give them "reasonable notice" to vacate (normally 2 months at the most).
If, for example, his wife refuses to leave after the expiration of the Notice, you would still need to issue Court proceedings against her to obtaina possession order.
It would have been beter for all concerned if a formal Licence agreement had been drawn up at the onset, so both parties knew exactly how they stand. You can still get such an Agreement drawn up now, if you wish, but the position when it comes to evicting your daughter in law will remain the same- whether a party has a Tenancy or a Licence, Court proceedings are required to obtain a possession order if the occupier refuses to leave.ie if she refuses to leave.
I would certainly hope this won't be necessary.
I hope this assists and sets out the legal position.