This phrase is used here to mark the beginning of a new part of the story. If your language has a way for doing this, you could consider using it here.
## while all the people were being baptized by John ##
The phrase "all the people" refers to the people present with John. This could be translated as "while John was baptizing all the people." (See: [[rc://en/ta/man/translate/figs-activepassive]])
## Jesus also was baptized by John ##
This could be translated as "John baptized Jesus, too." (See: [[rc://en/ta/man/translate/figs-activepassive]])
## the heavens opened up ##
"the sky opened" or "the sky became open." This is more than a simple clearing of clouds, but it's not clear what it means. It possibly means that a hole appeared in the sky.