"We are having dinner with Duo."
Translation:Duo ile akşam yemeği yiyoruz.
Just adding to what ArdaS_H already said, they are different things. tuzlu, şekerli are adjectives, they mean smth like "salty, sugary" (but in this course they're translated as "with salt, with sugar" because english can't use that mechanism for all words). so their -lu, -li suffixes aren't the shortened "ile" suffix meaning "with", they're the suffixes for adjective formation (lü, lu, li, lı)