Encompass and comprise are not interchangeable. Encompass means "include comprehensively" and comprise means "make up, consists of". - Google.
In the first sentence, encompass means "the festival contains music, theater, ballet, etc". You could not use comprise here because "the festival isn't made up of ballet and literature".
In the second sentence, I wouldn't use comprise here either because "the kingdom Plantae contains" makes more sense than "the kingdom Plantae is made up of". However, I think it would be acceptable to use comprise in the second sentence.
The kingdom Plantae is comprised of water-dwelling red and green algae as well as terrestrial plants.