1st grow need help 4 weeks into flowering

i have 4 GDP almost four weeks into flowering. I got the clones from a medical club. I'm using fox farm soil and fox farm big bloom with molassas. they are under a 400 watt MH with 200 watts of soft cfls as supplemental. This is my first indoor grow and things were goin pretty good until today I found that two of the plants have seeds in most of the buds, but none on the colas. Of the four plants the two that have the seeds are almost twice the size of others. The shorter plants are actually further along as far as amber trichs and orange hairs. however, they seem as if they have not been pollinated. I do not understand how half of my crop has seeds and the other half does not. I check my plants for hermies regularly and have found no pollen sacks. So my questions are: could they have been pollinated from a male plant somewhere outside? and is there a chance that the two pollinated plants could pollinate the other two? I live in Humboldt so there are plenty of other growers around. thanks a lot.

def could be the case you should look into some filtration from your outside air source even to just pull it from another room in your house( assuming you are pulling direct from the outside bummer though man better luck next time