hello cip, thank you for taking time off to read my post. i think you and all other goanetters should not take this caste business seriously, which is in any case, in this modern electronic age , is nothing but arrant nonsense.
interested, may be, for the sake of intellectual curiosity and may be, more for the entertainment it provides. the word twiceborn ( in sanskrit - dwija , actually meaning more than once ) is rather a misnomer. a soul (i.e. divine spark that escapes from god's energy) roams all over the universe having many many births, deaths, and rebirths not only as a human being but in animal form as well from an ant to an elephant. the divine spark rejoins god's ethereal form once it becomes free from all world impurities i.e. moksha. as to your other queries, i append below few quotations from manusmriti which are self explanatory in para 4 chapter10 : the brahmin (priest) , kshatriya ( ruler ), vaisya ( trader/farmer) are the three twice born castes, but the fourth caste the sudra has only on birth and there is no fifth caste. para 6 to 10 : children born out of mixed caste marriages 1) brahmin man and kshatriya woman 2) brahmin vaisya 3) brahmi sudra 4)kshatriya vaisya 5)kshatriya sudra 6) vaisya sudra children begotten by these 6 marriages are traditionally regarded as outcasts which is the fifth class (not caste) para 11 to 13 then there is the sixth class that of untouchables.; these children are from marriages in the opposite casteist direction 1) vaisya man and kshatriya woman 2) vaisya brahmin 3 kshatriya brahmin children ( although technically untochables ) of these three marriages are treated rather delicately as they happen to be from the males of the higher castes. 4) sudra man and vaisya woman 5) sudra kshatriya 6) sudra brahmin children of the ( 4-6 ) marriages are considered to be untouchables and the child of the sudra man and brahmin woman is considered to be the worst untouchable of them all. antonio ps. dear goanetters, please give some more time to answer your queries