If there is paternity test between the elder sister and the younger brother, it can only be determined whether there is blood relationship or kinship relationship. According to one of the paternity tests, it can be preliminarily determined whether it is the same father or the same mother. But if it is between half-brothers or half-brothers, this kind of paternity test can't be carried out because it can't be identified.
In fact, it is very simple to do paternity test, that is, to suspect that the child is not his own and that his wife is having an affair. That's why there is such a request. Many people don't trust their wives, so they always wonder if there is anything wrong with the address. When there are more and more such thoughts, he always feels that his children are not like himself, so he will have the idea of secretly doing paternity test.
In fact, this idea of wanting my sister and brother to do paternity test together is very wrong. If you doubt which child is not your own, why not have a paternity test with that child directly? Why should a paternity test be done between two children? If it is a paternity test between adults, shouldn't the accuracy be higher?
I think husband and wife are a relationship that needs to be promoted very much, so if you get married, I think you should trust your other half relatively. If you don't trust your partner, then your marriage is doomed to be a tragedy and certainly won't last long. So trust your wife.