If the numbers come up 1000 overgross, then its time to double check the calculations. Are you overweight for takeoff performance? Predicted Max landing performance? Or simply the max takeoff weight? With the first two scenarios, there might be something that you can do to come back into the performance envelope (IE change the TO flaps or runway or other configuration for takeoff/runway/climb limits or fly lower enroute if you're projected to be above max landing weight when you arrive). If it's the latter and you're over max takeoff weight, you'd better be figuring out a way to correct the issue prior to departure.
If the captain doesn't do anything, I'd tell him that I wasn't comfortable with the situation. If that doesn't do anything, I'd probably then simply inform the gate or ops that we needed to take a few passengers off the aircraft prior to departure. That solves the problem. You can always discuss it with him/her after the people are removed. If it really becomes an issue, call the Chief Pilot on Duty.
As for the 1400 RVR, remember that there are different criteria for when you have to have the prescribed minimums... when does it hit 1400? At the FAF? Prior to it? After passing it? Only if it is below minimums at the FAF do you have to discontinue the approach. If it drops below minimums at that point, simply announce missed approach and follow the appropriate procedure (and the same procedure as if the CA refuses to go missed at MDA/DH with no runway in sight).