I had an opportunity to watch a den of foxes who made their home in a busy neighbor backyard. What was unique (at least to me) was that the den site housed two families of foxes. Seeing this, I researched the probability of  red fox families sharing residence and was surprised to learn that it is a regular occurrence.

The reason for suspecting a den site with double occupancy was there were nine kits running around that were clearly two different sizes.

It was nearly dusk when this pic was taken. The foxes were very active with play. This pic shows the dominance and which pup stands where in this pack.

This kit appears to be a little bigger

Jim