Trees - Pine trees and other coniferous trees are actually already decently suited to this setup. Their seeding usually depends on fire and not a normal spring thaw seed that many other plants use, which means prolonged winters are not a threat to their reproduction. We already see much of this in the north. That said, these trees need the root structure and therefore can't survive in tundra/marsh and will be more common in mountainous terrain. Trees that loose their leaves wouldn't fare well in this setup.
Bush/shrub. Take from the current tundra, there are some hardy plants out there. Moss and the sort also tend to do quite well out here. I believe you will see some berry plants (wild blueberry) capable of surviving the elongated winters as well, some adaptations to the seeds to stay dormant until the summer phase appears will likely allow for berries to exist in these setups. I don't think 'raspberries' and other semi-permanent bushes would do well.
In both the cases above, it's likely these plants will support very expanded root systems for storing reserves through the elongated freezes.
I believe hibernation is out as a survival technique...the lack of definite summers pretty much rules out the store up fat and sleep option simply because the animal has no ability to guess how long it would be asleep for and how many reserves it would need to build up.
Life on land under ice - Ice is actually an excellent insulator and even in extreme cold, under the ice can still be inhabitable. Given the prediction of the expanded root systems, there should be additional nutrition to be found under the ice. Lemmings and other rodents could survive under the ice along the southern areas of this winterland.
Life on the land, herbavores. Migration has always been a valid technique for animals. That being said, it's 'seasonal' migration based on a constant cycle...if the season instant predictable, then these animals are going to need to adapt and find food locations during the extended winters, while still having a trigger to go back north. If there are larger herbivores wandering around the region, they will likely be migratory.
Life on the land, predators. I believe wolves living on the southern areas hunting both migratory and creatures under the ice should be able to adapt to these situations.
Life on sea ice. Honestly, I don't think theres much of a change in behavior here. If you have frozen over sea water, life on and off the surface will not have the cyclical nature it currently does, but I suspect the life (seals/fish/whales/bears) would not be greatly effected.
I live near the rocky mountains and am very familiar with the spring melt off. Winter snow packs up during the winter and when the warmer temperatures come, the water melts and the rivers greatly increase in volume and speed. With some rains added, we've seen some vicious flooding over the last decade. I would imagine a prolonged 30 year winter cycle jumping straight into a summer cycle would create some outright vicious flooding as the snow pack melts...rivers seeing 50x volume and low laying areas becoming completely waterlogged.