I have limited space in a mobile home park. we planted a dwarf fuji apple tree in our small yard but I want to plant a miniature red delicious apple tree in a large pot on my deck.

The Fuji is about 20 feet from the deck. If the fuji (distance) will not work to pollinate the miniature red delicious, could I plant another miniature red delicious to pollinate?

I believe 20' is plenty close enough for pollination. My neighbor has an apple tree that gets fruit every year and the closest other apple is across the street and 2 doors over.

You need to make sure a second apple tree is in blossom at the same time as your Fuji tree. Apples usually need to be in the same pollination group, (i,e, 1, 2,or 3) unless they are stated as being self-fertile.
As Zencat mentioned a neighbour's tree will act as a pollinator if it flowers at the same time as yours