Enjoy!
Senior martial brother - I thought it might be worth mentioning that this term has 6 syllables in English but only 2 in Chinese. This makes the English translation always feel quite formal or lacks a sense of urgency whereas that's not always the case in Chinese. This occurred in earlier chapters as well but I felt it especially in this one.
Spiritual soul - Could also be translated as 'spiritual heart' or just 'spirit'
Spiritual palace - The literal translation is 'purple mansion' but can be translated as spiritual palace. It refers to the location in the body where spiritual qi is cultivated and stored, might be another name for dantian?
Life spirit sword - Could also be natal spirit sword or destiny spirit sword. The general idea is that its a spiritual sword that is deeply linked to a person.
Not looking good for fourth bro...
A bit late of me but spiritual palace is pretty similar to the western term 'mind palace'. It is that pure black space that our twins have been talking to each other in.
For the martial brother stuff, would you guys (translation team) consider changing over to shixiong, shijie, shimei, shidi? (M.big bro, big sis, lil sis, lil bro, in that order) May need to add some TL note, but those 4 are more commonly used in EN ver of wuxian novel.