The other answers are great, so I'm going to fill in some misconceptions in the question.
SEND A SCOUT FIRST!
Building and launching a ship with 50,000 people on board, and their life-support, for a 4 light year journey where they need to slow down and land at the end is a massive undertaking. Doing it with little information about where you're going is a risk you do not need to take.
While that's going on, make some small, fast, one-way robotic scouts and send them out. It can make some observations, answer some basic questions, and send the intel back. The composition of the planet and its atmosphere. Is there life? Is it intelligent? Is it hostile? Do we need weapons? What's a Kardashian and how much delta-V do we need to keep up with them?
Even if the colony ship launches before the scout reaches Earth, the data from the scout still gives the colony ship, with the help of the people back on Alpha Centauri, years to better prepare for the landing.
We can make weapons to hunt animals from materials on that planet
You can hunt them, but you probably can't eat them. Meat on Earth is useful as food for humans because humans evolved from Earth. We share the same amino acids and vitamins as the rest of life on Earth.
In fact, we're so hooked into the rest of life on Earth that we're dependent on eating other life to get some of those amino acids. We're so interdependent that there's some things we cannot digest, we need bacteria in our guts to digest it for us.
A life form that evolved on Alpha Centauri, even if it's using DNA and amino acids, will have evolved to use a completely different set of amino acids and vitamins. Even if they fill the same roles (they probably don't), they'll be at least slightly different and their bodies will not be able to use them. At best they'll be indigestible. At worst they'll be poison. They'll also lack our gut bacteria to digest things for us.
This isn't just a problem for eating animals, its a problem for eating anything on Earth. And this applies to all life coming from Alpha Centauri. Earth life has evolved to make use of, or at least tolerate, the trace elements present on the Earth like Molybdenum and even Arsenic.
Aliens from Alpha Centauri will have its own mix of trace elements, and its own trace needs and levels it can tolerate. It won't be the same as ours.
Life has evolved to deal with a certain amount of trace minerals naturally present, but no more. More would be inefficient, and something better optimized to the environment would have an advantage. This is part of why industrial pollution of heavy metals is so toxic to everything on Earth, we've changed the mix of trace elements faster than evolution can adapt. People from Alpha Centauri will also have no time to adapt. Something in our mix of trace elements will likely be above their tolerance levels, and something they rely on will likely be too low.
Farming, hunting, and even breathing will slowly kill them and leave them deficient. They'll need to filter and supplement everything.
They can 3D print the weapons, but to make bullets is quite complicated, so they still need to pack at least the bullets
You have this backwards. Making bullets is easy, 3D printing a gun is hard.
Brass cartridges haven't changed much in over 100 years. Molding bullets is trivial. Making smokeless powder is also trivial for a space-faring civilization. Drawing a modern brass or steel cartridge is harder, but not difficult, and they can be reused and reloaded. At minimum, you can make paper cartridges. We figured this all out almost 150 years ago, and the Alpha Centauri folks can be safe to assume they'll find material on site to make bullets.
In contrast, a gun has to withstand the high pressures of the exploding powder. If you want it to be accurate, it has to be machined to high tolerances. If you want it to be semi-automatic, it requires fiddly little parts. If you want it to last, it has to be hardened in the right places.
We can 3D print a modern gun, but we only got this working in the last few years. And they'll will only last for a few hundred rounds, as opposed to tens of thousands for a normally manufactured gun. Improvements in 3D printing will fix this.
Point is: making bullets is easy and very well understood and we've been doing it for over a century. 3D printing a gun is hard, and they're not the best quality, and we only recently figured it out. If you can 3D print a gun, you can most definitely make bullets.
Since every additional gram of mass will add many, many times its weight in fuel, any "weapon" they bring with them will actually be a tool that can serve as a weapon in a pinch. If they need real weapons, they can 3D print them.