Since there will be single European foreign policy, they should only get 1 vote in the UN and NATO
Right on. If this is what they are saying, that they will be one united force, like all the states of the USA have one fedral military, then also they will only have one contribution to Nato, like the USA does.
It stands to reason that they also have only one vote and voice in the UN. The EU, is after all, going to be several states united under one body, just like the USA is.
We should in fact DEMAND that the EU have only one collective voice within the UN. Or else the USA should have 50.