After everyone has gone through the fence one of the Russians is seen restoring some barbed wire however this wire wasn't there as the group made their way inside.
When they dig up the casket, dude is wearing an arc welding helmet while using a cutting torch. He would not be able to see out of it. Besides that, the casket is aluminum and a cutting torch does not work very well on that.
If William was infected by a highly contagious and deadly biological disease, the US should have incinerated him and anything he touched and not buried him in the backyard.
Why would the Russians risk two of their most valuable assets for a grave-robbing job? None of their knowledge or skills were required.