Welcome to BYC - to answer your query, we will need to know the age of the bird (weeks is best) - as what we see could mean male or female depending on whether this bird is, say, 12 weeks old or 16 weeks old.
It's hard to tell, what is the age in weeks? but going by what I can see the comb and waddles are looking very red and well developed which could suggest a cockerel but again not knowing the age its hard to tell. If the tail feathers are curling down and pointy this could also suggest a cockerel, If the tail feathers are strait and broad with a rounded end that would suggest a hen.
At that age, the amount and color of the comb/wattle would point more towards pullet than cockerel, but when did the comb and wattle start to redden? If they have been red for several weeks that would take you back in the cockerel direction as tehy'd have been reddening at 3 months.
This is all so new to me. My parents got them in April. We have 2 white ones and 4 brown ones. If they are male, should we separate them from the females?
If you did not intend to breed and there is evidence that your males are causing more harm than good then yes separate them. I would say that the bird in question is in fact female. (A female chicken under a year of age is called a pullet, a hen is a female chicken over a year of age) The redness in the comb at this age does not matter but the size. If you got them in April than they are reaching their point of lay, which basically means when they start laying.
If you didn't know the chickens behind you are called Brahma's. They are not brown but Buff Columbian (Buff is a color while Columbian is a pattern). If you ever have doubts about gender you can look at the fold's of skin under their throat known as dewlaps. Only females should have them and it's easy to tell at this age.
Welcome to BYC and I wish you the best of luck with your chicken and hope that you can learn as much as you can about the wonderful world of poultry.