...over the space of a few generations what would be the effects would it take on living organisms such as humans and animals?
They'd all die. A few humans survive by reverting to Arctic living techniques, clinging to the equatorial coastlines and fishing from a ravaged and depleted ocean. Others might undergo a crash development program to survive permanently in underground bunkers.
All land dwelling life, including plants, not already adapted to permafrost would go extinct. Only sea life and lithotrophs (organisms which eat minerals) would remain. Even land animals which feed on sea life and are adapted to the cold such as polar bears and penguins would die from the extreme temperature drop within their territory and the extreme disruption to the ocean ecosystem.
To freeze all the fresh water on the planet you need to freeze the water at the equator, a place which runs an average global temperature of 30C and up. Global warming is already causing problems at a 1C change and will mess things up badly at 5C. Dropping the worldwide average temperature by 30-40C everywhere over a few decades would be so disruptive it would likely kill even land organisms already adapted to freezing conditions.
Even the Arctic thaws a little each year; not any more. The mean temperature in the Arctic goes from -10C to -40C. Land-animals shift away from their native areas too slowly to reach "warmer" climates 5000 miles away even over decades. Seasonal migratory species no longer have anywhere to migrate to.
With land-based plant life wiped out the whole land-based food chain collapses. Now it's a purely sea-based food chain. But dropping global temperatures will disrupt ocean ecosystems and currents as well leaving far less food available.
Arctic human natives would not be able to survive the extreme drop in temperature, disruption of their fisheries, and loss of land animals to hunt. They would have to migrate move south or die. Perhaps a few pockets of humanity would survive by adapting Arctic native living techniques near the equator if they could find people with the experience to teach them. Clinging to the coastline and fishing for whatever is left in a cold and disrupted ocean, it would not be pleasant.
There will, of course, be some people who will try to live underground. As we have yet to successfully figure out artificial permaculture, they would likely run out of stockpiles of food, energy and spare parts in a few years and die. Perhaps, given the temperature drop is over a few generations, a crash program could be initiated to learn how to permanently live underground, but given our track record of climate change denial I have my doubts.
This happened in the Earth's past, in a more extreme form. It's referred to as Snowball Earth. All fresh water and most of, probably all of, the surface of the Earth was frozen.
Global temperature fell so low that the equator was as cold as modern-day Antarctica. This low temperature was maintained by the high albedo of the ice sheets, which reflected most incoming solar energy into space. A lack of heat-retaining clouds, caused by water vapor freezing out of the atmosphere, amplified this effect.
Surprisingly, this didn't cause a mass extinction event. However, at 650 to 750 million years ago life was fairly simple and was largely confined to the sea. This was covered in an episode of Catastrophe.