my mother's sister married my father's brother. so, is their male children mahram to me, or is it not?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.

The children of a maternal uncle and maternal aunt and the children of a paternal uncle and paternal aunt are not Mahaarim (plural of Mahram: i.e. a husband or a person whom one is permanently prohibited from marrying due to suckling, marital, or blood relations) for a woman unless there is another thing which necessitates being her Mahram, like breastfeeding and the like. Therefore, the marriage of a paternal uncle with a maternal aunt does not affect by itself being a Mahram.

For more benefit on Mahaarim in Islam, please refer to Fatwa 85868.

Allaah Knows best.