Is it permissible for a brother to object to his sister's marriage to a Muslim man and to assault his parents because of it, knowing that the young man proposed to her, her father agreed, and his honesty was verified?

What your brother did by insulting and slandering his parents and by slandering your honor is not permissible. He should be advised, and his ill-treatment should not be reciprocated in kind.

There is no harm in a young woman speaking to a young man out of necessity related to marriage matters, provided that the accuracy of his statements is confirmed. However, a marriage contract cannot be concluded via the internet or phone; rather, it must be done through an authorization from the husband or the guardian.