Why did Yosef ask separately about "their Shalom, and the Shalom of their elderly father?
Seforno: Because old people are not generally well off - they become hard of hearing and have difficulty in speaking. 1
Ohr ha'Chayim: It is proper to first ask the Shalom of those present, before of those not here.
See Gemara Shabbos 152a.
Yosef asked about the Shalom of their father. Why did he also need to ask if he is alive?
Ohr ha'Chayim: It was one question - does he still have his strength? This is why he asked first about his Shalom, and afterwards whether he is still alive - i.e. is he like he used to be?
Ha'amek Davar: First he asked, is he b'Shalom with me, or angry with me for demanding Binyamin? We find like this in Melachim II 9:22,31. Then he asked if he is Chai, i.e. healthy. He wanted to know whether or not Yaakov can bear Binyamin being detained. They did not understand; they thought that he asks amidst love.
Why did Yosef call their father "Avichem ha'Zaken"?