What breed is this?

Look kind of like my brown Chinese babies.  Watch them as they get older they will get a knob at the back area of their beak if they are the Chinese or African.  Another possibility would be Troulouse but the females have orange beaks and the males black beaks.  I am not too familiar with other breeds so maybe someone else will know.

This will help you determine if it's a african or Toulsoule 

http://metzerfarms.blogspot.com/2011/03/how-to-differentiate-african-and.html

They look like a slightly less chunky version of my african babies at that age.  So precious!

The only way is to vent sex, which I have no idea how to do safely.  Your geese will love to free range (they graze on grass just like horses), and if they are africans, will make great alarm systems for your property.  I must warn you, though.  They are a more aggressive breed and you need to firmly establish alpha status with them from the beginning so they respect you.  Keep an eye out with them around your chickens. Hopefully they will ignore them, but it may be best to keep them as far separated as possible.

You'll find that as they get older it will be pretty easy to tell which is which . . .  generally speaking the biggest goslings are males, but I have one male gosling that was the biggest as a gosling and is now the smallest gander, so there's no telling. His mate outweighs him . . . but when they got to their first breeding season, there was no doubt who was male or female -- when the males are all hissing and need attitude adjustments . . . and the females are standing behind them being protected . 

There is a way to check gender by a blood test, but I think it requires them to be older.   It is also expensive.  I'm not sure about that one - remember that I saw mention of it in one of the posts here but not sure which one. 

I think all geese make good alarm systems -- mine are American Buff and Toulouse and are great at alerting us about issues outside . . . and all geese can be aggressive - some are just more hard headed about it.  Read the thread on the goose forum about how to discipline a gander, and try hard not to handle them too much as goslings -- it is hard, I know, but it will be worth it . . . the one I handled the most is the most difficult of the three ganders that I have. 

We have our geese with chickens and have never had a problem.  They are fenced into a large area, with moveable fence so they can have access to more grass (you will be amazed at how much the goslings eat!  Give them lots of grass!  We scraped up patches of grass every day for them and it was gone by morning) , with a couple of kiddie pools for fun, and the geese mainly ignore the chickens.   Some roosters might even be able to chase the geese around . . . but be sure to watch them carefully when they are first introduced and especially during the breeding season.  The chickens have their houses and the geese generally prefer to be outside . . .  our fence is electrified so I let them choose usually.   You'd probably want a house by the chickens for them and then they could all be shut in at the same time. 

We have a seasonal pond, and take the geese for walks down to it.  It is too big to fence in with our fencing, but they sure enjoy their swimming breaks.  Just make sure you have a way to get them to come out of the pond . . .