This is a really difficult situation, because of your changing household. A sighted dog requires constant monitoring & adjustment, but you are dealing with a dog who is not only blind, but newly so, & working to adjust to things as they are. Add in the other 2 dogs & the guarding aggressions, and you have a mix for a mess.
One thing I would say for certain is that your dog should NOT stay in your household. I'm sure you love him to pieces, but as someone who has had to keep dogs separated in my own household, without children/babies, & in a home that is set up FOR dogs, it requires a lot of constant attention, & awareness of changes in behavior & the ability to modify the set-up or schedule to accommodate the dogs.
Losing his sight has caused your dog to have fear reaction, which is leading to the growling towards your other dogs, & it certainly doesn't make him trustworthy around your child. This doesn't mean that he is an "aggressive dog", simply that he is having trouble responding to the changes in his health, and it has changed his "order" in the pack that makes up your household.
If possible, he could be rehomed. But that would require a very specific home - preferably someone without children or other animals, who would be willing to make adjustments to their home to accommodate his navigation needs, & is understanding of the communication needs for a blind dog.
Chances are, there are few if any homes like that who would be willing to take a senior dog. So please screen homes carefully, or even work through a shelter.
Whether or not you should euthanize him is a difficult decision, because he is in otherwise good health it sounds like. However, he is NOT compatible with his home environment, and that is stressful to him, as evidenced by his behaviors towards the other dogs & your son. If you aren't able to find a shelter/home for him by the time your newborn comes, you might be faced with that decision.
Not the easy "do this or that" answer that you may have been looking for, sorry. But in this case, you will need to do what is best not only for him and for your household. I would consult with a shelter in your area to see what they can do to help you. Best of luck. T.