I would recommend something classic and not too trendy, since you want the photos to stand the test of time.
If it helps, we did family photos last year for my parent's 50th anniversary. We did matching outfits, two different versions, one with women in LBDs/men in tuxes, and the other set with everyone in blue jeans and white collared button downs. I really dislike wearing white button downs and rarely wear them in my life, but I have to say, hands down, that was the best. The white looked flattering on everyone; reflects the light on to your face, makes your teeth look whiter, etc. The long sleeves were flattering on all ages. You see everyone's faces rather than their outfits. And, it's a classic look that won't date.
