Normally yes. VA disability will not affect your SSD payments. Your SSD will be based on how work credits (or basically how much money you have paid into the system). If you have paid adequate money into SS to receive SSD (or SSDI) you can receive both. He can receive it for himself and slightly more for each child under 18.
There are lots of places to find info on the web, It's unfortunate that the VA website doesn't make this data readily apparent. Here's one site with some more data.
How Much in Social Security Disability Benefits Can You Get? | Disability Secrets
Having gone through both systems, I would recommend to everyone that you have a lawyer help you with you SSD application and any appeals to your VA decision. I was (am) bedridden, on O2, unable to even get into my electric wheelchair to go to eat with my family and I was rated at below 50% for the VA and not eligible for SSD (dispite over 15,000 pages of medical paperwork saying otherwise). It took a lawyer to put the correct wording together and was well worth the money I paid him. The system sometimes works and other times doesn't. It can be a lifelong benefit. Have them talk to a VA/SSD lawyer.