The APA standard of perfection states that Rhode Island Reds are: Cock 8 ½ Lbs; Hens 6 ½ pounds; Cockerels 7 ½ pounds; Pullets 5 ½ pounds
There is no standard for Sex Links, since they are not a breed. So I will use the description from a hatchery for Black Sex Link chickens...
The average for a pullet to start laying is about 22 to 24 weeks.
Your Black Sex Links will probably start laying very soon. The Brahma will probably be the last one to start laying.