Why can't two daughters of one family marry two brothers of another family?

Maybe there are some customs in your place, such as bad feng shui at home. In my family, the custom is that the woman goes back to her parents' house to sleep with the man after marriage, before marriage. It's not good for my brother to have a baby at home. Later, I got married. In my parents' mouth, everything that costs money is said to be bad for my brother's feng shui (not free to eat and drink)