I am so happy! I did look at their vents one is definitely a pullet the other looks like a cockerel.
Vent sexing generally does not work on chickens (exception: day-old chicks at a hatchery, being sexed by trained professionals.) There are plenty of how-to articles for vent sexing ducks and geese at any age, because the males of those birds have a penis to see. A rooster doesn't have that.
For adult chickens, the vent of a hen that is laying eggs will look different from the vent of any non-layer. But a rooster and a non-laying hen (broody or molting) will have vents that look alike.
So I think your vent sexing probably did not work. I would guess that both of yours are pullets, but I can't be certain at this age (especially since you do not know what their current age is.)
At what age did you start the flock raiser/all flock and oyster shells?
Flock raiser is fine at any age, and so is chick starter. You can use the two interchangeably for growing chickens and for adult chickens. (Exception: if the flock raiser is pelleted, it cannot be eaten by very young chicks because the pieces are just too big for them to swallow. Chicks can eat flock raiser that is sold as crumbles, and older chickens can eat either form.)
Oyster shell can be offered in a separate dish, starting any time you want. They need it when they start laying eggs, but it should not do any harm to have it available earlier. Chickens are usually pretty good at eating the right amount of oyster shell.
When can they get meal worms thing like that?
They can have mealworms at any time, but don't give them too many. Mealworms are high in both protein and fat, with the fat being a potential problem if the chickens eat large amounts.
The chick starter or flock raiser should be their main food. If you want something that feels like a treat to them, but is nutritionally balanced, try putting a little bit of their normal food in a dish and adding water. Most chickens really like this.
They can start laying at around 16 weeks correct or is that misinformation? We want to get their brooder boxes ready soon.
Some chickens start laying as early as 16 weeks, some others wait many weeks longer. Chicks that are growing up in the fall will sometimes wait until spring to lay eggs, even if they should be "old enough" sooner.
You can get the nestboxes ready any time you want. Having nestboxes available will not hurt the chicks in any way.
"Nestbox" usually means a box where a hen lays eggs. It is often about 1 foot each direction, although other sizes can also work fine.
"Brooder" usually means a place to raise young chicks without a hen. A brooder needs to be big enough to hold food, water, chicks, a heat source, and space for the chicks to run around and play. It is much larger than a nestbox.
We think they possibly are Australorps but have no idea after hours of looking at chickens online! Any help with breed, age and sex is a huge help!! We want to care for them the right way. We want to add 4 chickens in the spring also so we want to make sure we get the right compatible chickens for them.
Almost all chicken breeds need the same care, and can live together without trouble. It is nice to know the breed, but it does not really change anything about what they need or who they will be happy to live with.
Your chickens are not from any breed that needs special care. All the ones that do need special care have easy-to-recognize traits that yours do not have: different texture of feathers (Silkie or Frizzle), or feathers over the eyes (some crested breeds), or unusual body shapes (round fat Cornish Cross), and so forth.