Sally, sorry about the situation you find yourself in. With the family history of PCa it does sound like a strong candidate, but try not to get too alarmed about it. With the low PSA, if it is PCa it's probably been caught at an early stage, and localised prostate cancer (ie cancer that's wholly contained within the prostate) is very treatable, and VERY unlikely to kill your husband. His life will be changed, but you'll still have him.
The time between the initial PSA test and the final diagnosis is very stressful, and it may well take two or three months before the final diagnosis is in. What I'd strongly recommend is that you DON'T consult "Dr Google" and that if you have any questions you phone the PC-UK nurses. They are wonderful and kind people who will be happy to talk to you for as long as and as often as you need. This next few months are going to be tough to get through, but you'll feel a lot better when you know what's going on. Uncertainty is the worst thing of all to get through.
Very best of luck to you,