Of course you have to agree to the UN Charter before becoming a DPI NGO, just as you have to agree to the terms the IRS lays out for tax exempt organizations before becoming tax exempt.
That doesn’t make jws anymore part of the UN than it makes them part of the IRS.
The issue is whether or not, in 1992, what they agreed with when this happened, violated their beliefs.
Once you show that, you have a legit argument.