Why Ramcharitmanas 6.61 mentions Lakshmana as his mother's only son and Raama's sahodara bhraataa?

Question

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?

Answer 1

From this answer, I found Bhavartha Bodhini - Shree Ram Charit Manas - By International Ram Charit Manas Research center which provides answers to these questions:

Why Lord Rama calls Lakshmana as his सहोदर भ्राता (sahodara bhraataa: born from same mother) when he was born from different mother?

The above Hindi commentary says that as both Raama and Laxmana born from same kheer, so in that sense they are sahodar bhraataa.

Also, Lakshmana had a brother named Shatrughan, so how Lakshmana could be his mother's only son?

The above Hindi commentary says that Lakshmana was not his mother Sumitra's only son but prominent son. And another reason might be thaty Lakshmana regarded Sita as his mother and by that time Sita had no children so he was Sita's only son.