I found out based on my research that there is quite a number of female choirs around the world who perform very well. Basically, female choirs have their own choral arrangement meant for their voices alone but I’ve heard of one female choir singing SATB arrangement which is so nice to hear. There are certain rules in choral singing. There should be no overlapping of voices but when i heard them sing, notes were not following the rules. This is musically beautiful but theoretically wrong.......what can you say about this?

I don't think there are ironclad rules. If you want, you can have a flute and a trumpet play the same melodic line, accompanied by a soft harp. And there's nothing against it.

Strict rules work only when you are at school learning about music theory. That was the case of the penalized parallel fifths and octaves.

I beg your pardon for my excessive haydnism, but I remember a little nugget I read in one of his biography, which, by any hazard, I own...

Haydn added conciously a little error in his trio (symphony # 101) that he changed at the end of trio when a similar sequence appeared...

__________________
"Handel understands effect better than any of us -- when he chooses, he strikes like a thunderbolt... though he often saunters, in the manner of his time, this is always something there."

Mozart

The rule to not overlap parts is a traditional one (like all four-part harmony rules - parallel 5ths etc), and may be disregarded in our present day (which seems to have no rules at all).

Remember that rules didn't exist for Bach (on whose works most of these rules are based) and that's why you find these 'mistakes' in his music.

In the end, musical beauty is most important.

It also depends on the style. I would imagine that even in the all women's choir, there's not a lot of voice crossing, especially in traditional music. Remember that it's only considered crossing if the alto is higher than the soprano on preceding note, that note, or the next note, other than that, the alto can still sing as high as they want as long as the soprano stays just a little higher. And in that sense, you can easily have 6 or 8 parts in a women's choir with no voice crossing at all.

if it sounds good, it is.
rules are general observations/practices that did NOT come from the Lord.

dj