"We are standing in front of him."
Translation:אנחנו עומדים מולו.
There is some controversy here. What I think is the following :
Opposite, across and facing are pretty similar in English. The choice of one over the other would be some kind of nuance or personal preference. They translate to מול.
Before and in front of do mean, implicitly, that I'm facing something (because otherwise it wouldn't be in my front) but are more positional inclined, they translate to לפני.
The words מלפני and מאחורי are in front of and in back of (or behind), but not before it after.
The first group has a certain relativity, between to objects. The second two are absolute, or at least, referencing a system external to the objects.
Some might disagree with what I just wrote.