Problems with houseplants?

[pachyrhinosaurus]

As some of you know, I grow rainforest plants, I have some from South America, Africa, and Southeast Asia. I am having problems, though. My bananna trees seem to be dying and so is my King Sago. My bananna tree keeps growing new leaves and they keep dying. They also are very small. They are less than 30 centimetres. I saw one at the freenhouse, which arrived in the same shipment as mine, is at least a metre tall. Meanwhile, my King Sago's leaves are dying. There were little leaves, which died and I cut them off, and bigger leaves that are browning. I do know it is winter here, and things get a little abov freezing. This is my King Sago's second winter, but my bamnana trees' first.
What Should I do?