Very Scared Adopted Dog, Any Advice?

6months back i found a 1.4yr old, male papillon on the street and adopted him, he was a wreck in the begining, when we would go to pet him he would lay down and wait to be hit, he had major seperation anxiety and it was hell when we had to leave the house to go to work even though he was not alone (we have a female maltipoo same age as him, been with us since a baby). well he is still scared alot, they pee and poop on a balcony we do not use and as soon as the sun sets he will not step foot on the balcony, instead he will pee and poop all over the house, so i started going out with him and trying to keep him on the balcony until he does his business, hes house trained just too scared. any noise will freak him out, a car, our christmas lights on the christmas tree, anything at all, he is even scared of a fly.
anyway my parents took him and our maltipoo out yesterday and they had to come back after 15mins (btw our adopted dog is very very hyperactive and when we take him out he gets so excited that he finds it hard to breathe and cant catch his breath) well anyway when they took them out yeasterday they told me that the papillon was uncontroleable he kept jumping and insanely barking at people, no one could pass by him without him barking his head off at them and our maltipoo started doing the same ( she is usually a very very calm dog and only barks at other animals, she is extremely friendly and just a sweet heart) but yesterday she also started barking like crazy at everyone, that she drove my mom to the point of bursting into tears, i walk them daily and they never do this, they are overexcited the firt 5-10mins but then they are fine, the papillon barks only at children but i think that is cuz he was abused by them before, but my maltipoo is extremely calm when i walk her, i do not want the adopted dog to have a bad influence on our baby girl, how can i prevent this?
also what can i do to help him get rid of his fear?
and what can i do to stop their behaviour?
any advice will be highly appreciated.
thank u