Translation:I noticed a great brotherhood between them.
I don't see it as any more sexist than english. We don't get mad about having a 'wo' stuck in front of 'man' to make woman, thete's nothing wrong with adding 'in' to 'vir', either. It is as it is and that's fine. I do see a need for gender neutral options these days, though.
One can use the non official suffix -iĉo for man (like -ino for woman).
This is deducted from male diminutive -ĉjo (like -njo for woman).
If this would be widely used, then the word without -iĉo or -ino woulde be gender neutral.
Tio estas kion mi pensis. Ĉu vi jam legis "Seksa egaligo en la lingvo – laŭfundamente" de Cyril Brosch ? https://lingvakritiko.com/2015/01/31/seksa-egaligo-en-la-lingvo-laufundamente/
'Between' refers to two things which are clearly separated.
'Among' talks about things which are not clearly separated because they are part of a group or crowd or mass of objects:
First see the difference in english: https://wikidiff.com/content/notice-vs-remark-whats-difference-0
Mi rimarkas ion = I notice...
This is passif like "I see, I hear, I notice something".
Mi rimarkigis ion al iu = I remark...
This is actif like "I say, I tell, I remark something to somebody"