Sadness is a part of of life just as is joy and sometimes there are dark clouds and at other times bright sun.
For without sadness how would know how to cherish those moments when we aren't sad, those blissful moments would otherwise pass unnoticed, unappreciated. I choose to see the beauty in sadness, the beauty in loss, the beauty in leaving, the beauty in change, for it makes me appreciate life so much more, and not just take things for granted, neglect appreciating the being alive fact.
Them squirrels will definitely miss your family and the nuts they always got from you guys. They may not be able to show or say they love you, but deep down, whatever it is they feel towards their close relatives and partners, they do for you guys.
They will notice the change, but hopefully where you guys move to next, there will be new animals to befriend and take care of.
RE: The wild family in our garden.