There is no such thing as a 'Rabbit Cold'
It sounds as though the two Buns have an upper Respiratory tract infection. This is often caused by Pasteurella which is a bacteria most Rabbits carry in their nasal passages. At times of stress, eg time spent in a Petshop, overcrowding, bullying by other Rabbits, other concurrent illness, the Buns immune system is not able to 'cope' and symptoms of Snuffles (snotty nose, sneezing, gunky eyes etc) develope.
It can be a serious condition and whilst abx can bring about a relief in symptoms the problem can recur at anytime in the future and any prospective owner should be made aware of this so as they know what to look out for.
Left untreated Snuffles can progress to Pneumonia which is frequently fatal.