Are we sinful if we reduce our visits to our father who treats us badly and verbally abuses us, knowing that he differentiates between us and our siblings from his other wife and wants to take our pensions?

The father's shortcomings in his duties towards his children do not justify their disobedience ( 'uquq ) or their failing in showing him righteousness ( birr ), obedience, kindness, and maintaining ties with him. The Quran commands kindness to parents even if they are polytheists. Righteousness towards parents is an obligation without condition or restriction.