Why, then, ask your brothers and sisters to pray for you? or don't you?

The difference between you and Catholics is that they believe they can ask their brothers and sisters in heaven to pray for them, too. This is because of the communion of saints, as I indicated. The Catholic church teaches that Christians on earth and Christians in heaven are in communion with one another. And since Christians in heaven are therefore righteous, their prayers are especially efficacious. James 5:16.

I would caution you against carelessly accusing brethren of worshipping idols. If Catholics say they don't worship Mary or idols, then perhaps you are treating brethren as strangers and lost because of a difference you don't understand, a difference that in the end makes no difference at all. John 7:24.