Help with aggresion

Question
I recently adopted a 3 year old male yorkie, I have very little information from previous owner other than they had children and he had very little boundaries, supposedly never bit children (?) has not been fixed and one of the children accidently closed a sliding door on his leg awhile back, most of the time he is sweet and allows being pet and held, however has displayed at times aggressive behavior, the first time was when I was holding him  and my husband grabbed his little leg in a playing manner and bit him, after that he tried to pick him up while laying next to his feet and started growling at him, then my granddaughter was with him in the bedroom she tried to reach over to hold him while he was laying down growled at her and hid under the bed, today as he was laying down on the kitchen floor i tired to reach over and hold him so he could lay on his blanket and he snapped at me barely nipping my finger, what we have been doing is letting him be and let him get over his mood and come out of wherever he is on his terms, one other time I tried to correct him as he was urinating on the wall and he growled at me, I want to do anything I can to help this problem and try to figure out what it is that triggers the aggression , most the time he gives us a warning like saying leave me alone but today it got close, he did not hurt me just barely but I am concerned, I have been told he has too much testosterone and getting fixed might calm his aggression, he also only has one testicle, the other is internal, not sure if that contributes to the aggression.
I appreciate any feedback as I have a feeling this little guy has not had the best life and probably used aggression in past to protect himself as after the fact he shows remorse and tries to hide.

Answer
Hi Giselle,
Technically this dog is not a terrier. It is a Toy breed. In my opinion this is not a dog you should allow around children at this point.
There is no reason why this dog should not be neutered immediately and I mean tomorrow. Once the testosterone gets in the blood the behavior starts - neutering can calm him down tho it's not a guarantee but do it anyway. Especially if he is a leg lifter. Oh and get a belly band before he stinks up your house.
This is an alpha dog who may or may not be exhibiting fear aggression or may just have never been trained period and has developed some very bad habits which you have no experience in getting rid of.
I seriously doubted they told you the truth about his never having bitten before.  Peace and quiet may help and learn to correct the behavior by firm commands. No means NO. This can take a very long time - I hope you are patient.
He may still be hurt from the door incident, have a vet check him over to make sure it is healing and not in real physical pain. You may have to find a behaviorist to evaluate him.
hope this helps- it's tough to rescue dogs when they have this kind of behavior- they become boomerang dogs and that is sad in deed.
Good luck..