How would we politely say to a coworker: Will you join me at the (dining) table ? Would it be like this : "La unirà a me al tavola ?"
I assumne ti in the answer is a reflexive pronoun. If so then I think si unirà a me al tavola is the formal you. But I'm not sure you would use it rather than ti to co-worker. The use of Lei/tu seems pretty complicated.