Units do not block LOS/LOF.
Depends on whether there is any other blocking terrain!
Suppose there is no blocking terrain between attacker and defender, but there are enemy/friendly units. Is that LOS/LOF blocked by these units?
Basic rules, VII.B, first paragraph:
"If the straight line crosses any obstacle that blocks vision, then the line of sight/line of fire (or LOS/LOF) is blocked; if the straight line is free of obstacles then the LOS/LOF is clear, and the attacking unit has a clear view and clear shot at the defending unit."
Also, in VII.C, units are not mentioned anywhere as LOS/LOF Obstructions.
COWTRA - Concentrate On What The Rules Allow.