
I am aftaid that you will need to take them out sepoerately. Contrary to a lot of peoples hopes the yopunger dog does not help the older to be more confident, rather the younger learns to be afraid from the older.
This is the main reason when people want a new canine family member I always advise (from perdonal experience) that the older dog is trained and behaving as you would wish b efore a second one is added to the equation.
I have a friend who has a young bitch who is dreadful on the lead for fear aggresion, barking and generally acting up. Her new pup will not go out in public with her until she is cured of this, even if that is never.
Sadly this 17 month old bitch was purchased to keep her 5 year old male company, as her two old ones where unlikely to live much longer, sadly he died of Liver Cancer a month before on of the old ones, hence the new Pup.
It may be that your freind and yourself will never quite cure this baeking at strangers fear, but includeing another dog who will reinforce it, from copying eill not help.
I suggest that you take them out seperately, and you can then concentrate on being clam and matter of fact with them both. Do not pander to their feasr, but get th4em to focus on you and speak in a cheerful upbeat tone 'leave it' good boy, that's it look at me etc.
It will be harder work (two lots of walks) but it will be better for you and them.