Cougar are not solitary by nature..gps collars have proved that.
The 5th cat could be a son of the female or those kits father...she will kill for him or at least he will share in the kill just as the kits do. It is possible she has 4 kits...I have never seen that many traveling like that but three and a Tom I have seen several times...they even scavenged road kill together.
Biggest cat I ever killed was feeding off road kill along with a she and her two kits..the road kill had been dumped by highways. The cats here frequent the dump location. It is the best place to find a track. Especially a transient.