It saddens me that you didn't read the link I provided...So you gonna tell me that one of it will die? BTC or BU?
Both teams try to get the whole network for themselves, thus preserving the Bitcoin price for their coin. Right now Bitcoin seem to have more chance to keep it. But that's my personal opinion.
1. If I understand it correclty BTC will be same without any changes and blocksize will be max 1 MB right? And this blocksize is a problem for now and that is why they want to make BU right? If I am right it means BTC will die and new bitcoin will be BU true?
If nobody wins, current Bitcoin has indeed 1MB block size, which in some cases in not enough.
If BU wins this size will be increased.
If SegWit is activated many transactions will go onto an "additional place", so the 1MB may be fine. (This is an oversimplified explanation.)
2. What if i will want to send BTC to somewhere and I will not know wallet is in BTC or BU? Then I will lose it? Many companies will need to update their wallets to possible receiving new coins like BU right? So there can be many examples when someone will send BTC and receiver will not get it because will want to receive BU it is big risk dont u think so?
If your wallet will be on Bitcoin network / blockchain, it will send Bitcoin to a Bitcoin wallet.
If your wallet will be on BU network / blockchain, it will send BU to a BU wallet.
If your wallet will be an online service/wallet, you will have to research for yourself if it's BTC or BU.
3. If BU will be new coin so worth of BU will be growing very fast, then BTC will losing... so everyone who will keep money in BTC or BU will lose because i dont think so new coin BU will have same price like BU now or am I wrong ?
BU may inherit BTC price, may start low and go very high or will be a complete fiasco.
If I'd have a crystall ball, believe me, I would be rich already and would have better things to do than help you understand BTC and BU
4. When this hardfork will gonna to happen?
From what I know it's not a fixed date. It will happen when/if a huge % of the network supports the idea (there are some ways to tell that).
That's why I said that there's a high chance that only one of the two will matter after the hard fork,
if that will ever happen.
5. What if i have all my money in BTC in some exchanges like Poloniex? What is then?
If you have coins in online services, it's up to them. They can give you either BTC, either BU, either both, depending on their policy.
Poloniex has a statement here about what they plan to do if this happens:
https://poloniex.com/press-releases/2017.03.17-Hard-Fork/6. If I have BTC in my wallet where and how will i get BU ?
Export your private key(s), download BU wallet, import the private keys, sync.
7. What is the best choice to do now? Sell BTC and keep in cash? Sell BTC and keep in altcoins or what?
The best choice is to never get trading advises from unknown people over the internet.
I would say: think that there's (and will be) only Bitcoin an no BU. Invest (or not), keep (or not) in the same way as BU idea would not exist.
Whether BU hardfork happens or not, there's a huge chance your Bitcoin (or BU) will be remain at the same price.