I'm Miranda, and I'll be happy to try and help you with your question.
Unfortunately, wasps love to attack bees at this time of the year because of their need for sugar. They will definitely attack and often destroy weak beehives first, which is likely why two of your hives have died.
Entrance reduction to the hive is definitely the best thing to do to help, which I see you've already done, but make sure that the size of the entrance is reduced to the width for a single bee to get in an out. After doing some research, I've discovered that a lot of people are suggesting to add some form of tubing to the entrance of the hive. Try attaching a piece of tubing about six inches long and half an inch in diameter to the hive entrance. The bees seem to have no problem using it to get in and out of the hive, but the wasps don't like it because of the concentrated amount of bees that could be inside.
Make sure there are no other openings that the wasps are using the get in and out of the hive: sections where hive parts aren't fitting closely together, gaps around the roof, knot holes, etc.
Also, make sure the area around your hive is extremely clean. Make sure there is no garbage, rotting fruit fallen from nearby trees, drips of honey, sugar, wax bits, etc., around the hive because it will attract wasps in droves.
Another thing I discovered is that some people feed sugar syrup to their bees at this time of year, which is another thing that will attract wasps. The honeydew left by insects (aphids) on trees can also attract them.
Hopefully if the cold weather remains consistent in your area, the wasps will die off soon. They can't handle such cold temperatures for very long. The traps you have should also help kill off some of them.
I hope that answered your question. If you have further questions, please ask. If this information isn't helpful to you, please let me know, and I will "OPT OUT" so another expert can try to help. It's been my pleasure helping you. Please remember to rate my answer positively, as rating me is the only way I receive payment/credit for my work.