A pension does not have an account balance. The company makes annual contributions to the plan according to ERISA requirements. The plan can be overfunded or underfunded at any point in time. The employee contributes nothing. The pension commits to making payments to you after retirement. the amount is determined by the pension plan. You may be thinking of a defined contribution plan which is probably a 401k and which calls for periodic contributions by employee and employer. I never had one of these but expect there is always a balance known to the employee. The employee generally decides how to invest his money.
No you don't need to calculate it and do all that. It's whatever they send you. Say all of it is the RMD. If you have a RMD requirement it will ask you if it is the RMD. Say yes and enter the amount as the RMD amount. The pension doesn't need to calculate any RMD. Anything your pension pays you is considered to be the RMD. Traditional pensions automatically fulfill the rules of an RMD. So just enter the same amount in box 1 for the RMD for each 1099R.