Very tough decision in my opinion , I'd probably end up getting rid of either the blue dream or blue widow, even though both of those sound like great strains I think the others in comparison are simply better choices.
If the blue dream was doing noticeably better than the blue widow or vice versa health/plant structure wise I'd most likely take that into account of who I'd toss as well; depending also on your taste for sativa/indica, being a Sativa person myself and the already wide selection of indica dominant strains you have going, I'd probably keep whichever of the two was leaning towards being more of a sativa phenotype.
If blue dream is grown right it is oh so fantastic. I've heard of blue widow neither me nor my friends have ever tried it nor heard much about it . We've all been around a while and still never had it, guess that may mean something to someone lol