“All that is mine is yours” is an ironical statement of the father (who symbolizes God), because, first of all his possessions and belongings, to the father belongs his younger son as son, but the elder brother does not regard him as brother any more (for he already calls him not a warm “my bro”, but a chilly “your son”) so, he is no more his. Therefore, the father’s words to the elder son is an ironical reprimanding, as if saying: “all that is mine, is yours also, but you yourself, through your grudge and ungenerous, uncompassionate heart, deprive yourself of my most cherished possession - the love of my hapless son; thus, not only he needed repentance, but you too need it, and in fact even more than him you need it, for then you would also embrace him and only then indeed what is mine would also be yours, for I have nothing more valuable than all-forgiving love”.
As to restoring younger son’s inheritance at detriment of the older son’s share...oh, NO! And how, if they creep at all, such calculative, petit bourgeois and mercantilistic thoughts can even be entertained for more than a few seconds?! They are to be repelled outright even through a simple logic: that father gives to each their share, it does not mean he himself divests himself from all of his property, at least until he lives. Thus, he, out of gladness for the returned son, gives him not only the same share but even more - for before he was not given such a costly vestment and such a precious golden ring on his finger - but not at detriment of the older brother, for, as said above, the father wants also the latter to abandon his callous, judiciary attitude towards his flesh and blood and take share of his, the father's most precious possession - love of the son, his brother, and the father's joy for his repentance and return.