How do you say you both look good together in English?

What a great question! If you are talking about a boyfriend/girlfriend, husband/wife, or similar pairing, you might say to them, "What a great looking couple!" Or, just change what you said in your question a wee bit: "You too look really good together."

If the people are not that kind of couple, but they have dressed in similar fashion or look like each other you might say, "You look like two peas in a pod!"

Whatever you say, smile and show that you are glad to see them.