Since there is no international transit in the US, all will go first to passport control, then to baggage claim to collect bags, then through customs, then drop bags just after exiting customs. Upon exiting customs you are now "landside" or outside the sterile area, so you will all then go through TSA security again to get to your connection. Three hours is normally enough time for non-citizens.

At Dulles, all will walk from the plane over to the "moon buggy" mobile lounges (exotic, 1960's design shuttle buses) to be driven over to the International Arrivals Building in the Main Terminal for passport/customs processing.

At passport control there will be lines for citizens/permanent residents and lines for non-citizens (there is no line specifically for Chinese citizens), so your party would normally be separated to the respective lines. However, you should ask one of the line monitors if your party can stay together - they might allow it (and frequently do for "groups").

After clearing passport control you will pick up your bags, then go through Customs. There is no separate Customs Inspection for citizens and non-citizens - all go through the same inspection. Unless you have items to declare this is frequently nothing more than literally walking past inspectors. Upon exiting Customs area there will be airline customer service desks. If you are already checked in for the connection and your bag has already been tagged all the way through, you will just drop off the bag without having to spend much time in line. If not checked in/tagged through, you will have to stop at the service desk to check in and/or get new baggage tags.

After dropping off bags, you will exit out of Customs into the lower level of the main terminal building (the main baggage claim area) by carousel 15. You now need to go through TSA security to then go out to the gate for the connection. This is a short walk on the same level to the West TSA Security Checkpoint between carousel 12 and 13.

Pass through TSA screening and then you can take the AeroTrain, or walk or even take a mobile lounge out to Gate A. Depending on your timing, I suggest taking the mobile lounge as it will give a nice "unofficial" above-ground tour of the airport out to Gate A (as opposed to either the train or walkway which are underground).

Mistakes to avoid: arriving mid-late afternoon during international rush hour; not following signs carefully when navigating the arrivals building, having issues affecting admissibility or having issues with Customs.

Enjoy, have a safe trip!