They are in relationship to each other on a timeline but that relationship can be indicated by other things than tense. Tense changes are confusing. They bemuddle what you're trying to be clear about. Believe it or not, adherence to some rules actually frees you up to be more creative. Think of it as music. YOu can play any notes you want, but certain notes together make a pleasant, harmonious chord. THe ordered use of those chords make music that you want to listen to, whatever style you prefer.
Think of sentences as chords. You can do what you want, but some things will jar. Some will create harmony and joy. Within that harmony and joy, you can get your point across easier.