My inclination would be the Argyle and tie. I second the advice to ask your brother for clarification on what they are wanting. While the PC may be a bit over dressed, for a special occasion at church I'd not think it out of place. True to the theme of different worship cultures I was always taught to wear your best to church to honor God. I wouldn't wear my PC each time I went to church but would wear an Argyle. For weddings, funerals, or baptisms I'd go with the family's wishes.

YMOS,
Tony