Translation:They favour each other
Apparently no. That changes the whole meaning to "Wanapendana", because "kupenda" and "kupendelea" are two very distinct words. Just like their English counterparts, "to love" and "to favor".
When does prepositional form needed??? There are certain verbs we have to learn by heart?
To favour is to prefer something or someone more than the others, or to give unfair advantage to someone over the others. If a teacher favours one student they treat him/her much better than the rest of the students and unfairly gives him/her high grades. I hope that helps
Wanapendeleana "They favor each other" It's a bit confusing but, kupendeleana (to favor), kupenda (to love)