Why does the Torah see fit to insert the words "Ki Yamuch Achicha u'Machar"?
Rashi: To teach us that one may not sell his ancestral inheritance unless he is forced to do so due to poverty.
Da'as Zekenim: This enabled Yirmeyah to tell Hashem 'You fulfilled "Ki Yamuch Achicha u'Machar" (Yisrael were exiled due to transgressing Shemitah). Fulfill "v'Ga'al Es Mimkar Achiv"! You called Yisrael Your brothers
Why is there the prefix 'Mem' in "me'Achuzaso"?
Rashi: To teach us that, even when one is forced to sell one's ancestral inheritance, it is not correct to sell it all.
What is the meaning of "Go'alo"?
As in Rus (Ibid).
What are the connotations of "v'Ga'al Es Mimkar Achiv"?
Rashi: It means that if he comes to redeem it, the purchaser may not prevent him from doing so.