I bought a rottweilwer and he is 6 years old I have two chiujuhas and I have not...

[Allstate]

...introduced them I am scared? I bought a rottweilwer and he is 6 years old I have two chiujuhas and I have not introduced them I am scared?
I know nothing of this dog except it was left outside for all of his 6 years and he has major food aggression. Are rotts good with little dogs or should I get rid of him? I just wanted to save him from sleeping outside another night in the 20 degrees while it raining
1 hour ago - 2 days left for voting
Additional Details
I failed to mention that he follows me around everywhere. He seems attention starved and I can give him attention. I do have a 2 and 4 year old little boy and girl. He seems great with them. Should I be worried that he will hurt them? I do not know what to do. I just wanted to save him but last thing I wanted to do was hurt my chijuuas and especially my little children. Should I be worried for them?
PS he is a male and not nuterted. I am taking him to the vet tomorrow. I want to do some kind of temperment testing, and make sure he is healthy. All he does is pant too is that normal? I have let him outside to go potty and he does go out but does not really want to but I think he knows he has too.
22 minutes ago

one more thing, I tried to give him a hug a few minutes ago and he growled at me. why?
21 minutes ago

I also failed to mention my chijuhuas are in their own pack and are agressive twords other dogs unless we are at the dog park but even then (sometimes) but at the dog park they are really happy.
I would like to introduce them there. but getting them all there at once is not possiable because I can only drive one car, and the dog park is far from my house it is about a 30 minute drive. any suggestions as to where to introduce them? as soon as I bring them all in the house my chijuhaujas will attach him for sure. Will he ignore them cause there so little like most big dogs do or will he attack them? how long does it take a dog to settle into a new home and new surroundings ?