A man should not walk between two women standing close enough to each other in a way that it is considered passing between them. The same would apply  for a lady to walk between two men. Similarly a man or woman should not walk between two dogs or pigs. If one has someone else passing through with them, or if a man is holding onto his tzitzis, or even if holding any object, then it will be ok to pass through. If needed one could say a pasuk while they walk through and this will also help. One can be more lenient regarding sitting between two men/women, especially with family members.