Talking about a work done in the past, is it correct the sentence?
Yes, you would use "were" because it is the third person plural of the verb "to be" and the subject, "activities" is plural. The past tense of "involved" and "were" matches, so this sentence is fine as is.
Note that you should not use a colon before your list because it disrupts the flow of the sentence. See here for more on this.