Preaching only makes the task of giving witness more difficult if your preaching or behavior interprets to them as ‘you think you’re better than them’ and this may result simply in resentment.
It won’t necessarily even make the rest of the family feel guilty, just resentful of you apparently thinking you are better and more holy because you criticizing their behavior,. They will just be more sensitive to any sign that you think you are better than them.
People do genuinely move away from belief or practice for reasons you don’t necessarily know and they maybe can’t explain. You father may have a very practical nature where he has decided that the effort, too many uninspiring homilies, no effect from going to Mass in life, and he might have no guilt whatsoever so can’t be guilted into going, just feel indignant that you ‘preached’ at him.
Of course you felt you should try, but the best thing you can do is live the faith well yourself, and pray for your family. You may find it harder now that the family has the sense that, in their opinion, you appear to think you’re better than they are that you felt you could take them to task, especially, of all people, your father. So you may have to offer up any backlash or teasing if it is directed at you.
People don’t take to what some call "holy Joes’. I used to get called that at school even, because I always tried to do the right thing. It’s not pleasant to live through being an outsider in this way. Your prayers and faithfulness, as only God can really move souls and minds.
