I knew this time was coming, so it's not unexpected. We are prepared for it as much as one can be and cautiously looking forward: our home will bulge a little at the seams as my son and his family move in with us as they sell a home, buy a home, transfer job, etc. He is already here with us and his family will be here next weekend to visit and then later in the month come to stay with us while they are in transition.
It is not my first time having a child return home. Only my boys have come back thus far, both when leaving the service and getting established in their civilian life (or transition to another branch of service) and now. It's never too hard, nor easy as you'd hope. It is always a bit of a challenge and a bit of a fruit basket turn over but it works out.
One way I cope is to accept a small room and board fee. Keeping our budget in line is foremost and if that sounds mercenary, I will say in my defense that it's a nominal fee that literally covers the extra cost of food. My sons have always appreciated the fact of paying their way and at the same time of having home comforts. I try to strike the balance between the two.