In hindsight after the mite counts I should have pinched the two high mite count queens, combined my favorite with the larger colony and combined the other two. They may all have made it then.
I would be a pit causious about uniting colonies, that are having problems, with healthier colonies. There might be viruses and uniting can cause more harm than good. Good surviving colonies with low mite counts are best suited to make increase. I would leave the ones with troubles untouched, or carry them into one special yard of weak colonies. Sometimes some of them can suddenly start growing again, most of them will perish.