The younger brother may enter the room in which his elder brother sits with his wife. There is no fault to be found in this. If the elder brother enters the room where his younger brother is with his wife, then he acts against the rules of propriety.
गुरोरनुप्रवेशो हि नोपघातो यवीयसः। यवीयसोऽनुप्रवेशो ज्येष्ठभ्य विधिलोपकः॥