Ramcharitmanas 6.61 (Lankakaanda - Doha/Sortha 61):
सुत बित नारि भवन परिवारा। होहिं जाहिं जग बारहिं बारा।।
अस बिचारि जियँ जागहु ताता। मिलइ न जगत सहोदर भ्राता।।4।।
[Lord Rama to Lakshmana:] Sons, riches, wives, houses and kinsfolk in this world repeatedly come and go; but a real brother (or own brother or brother from same mother) cannot be had again in this world. Ponder this in your mind and arise, dear brother.
निज जननी के एक कुमारा। तात तासु तुम्ह प्रान अधारा।।7।।
[Lord Rama to Lakshmana:] Your mother's only son, you are the sole prop of her life.
Why Lord Rama calls Lakshmana as his सहोदर भ्राता (sahodara bhraataa: born from same mother) when he was born from different mother?
Also, Lakshmana had a brother named Shatrughan, so how Lakshmana could be his mother's only son?
Are there any commentaries or correct translations for Ramcharitmanas available?