When it comes to finding synonyms for the phrase "twin-brother," there are a number of options that you may want to consider. Some possibilities include "identical twin," "fraternal twin," "double," "clone," "match," "lookalike," "mirror image," or simply "twin." Depending on the context in which you are using the term, some of these options may be more appropriate than others. For example, if you are talking specifically about identical twins, then "identical twin" or simply "twin" may be the best choice. On the other hand, if you are speaking more generally or looking for a more creative alternative, then "clone" or "double" might be a good choice.