No, there is no need to reinstall anything.

Start Electrum. Then go to File > New/Restore. Name your wallet, click OK and then the wallet creation wizard should pop up. Choose the option to "Restore a wallet or import keys". Then follow the rest of the instructions in the wizard.

You should see the address in File > Receiving Addresses.

With the seed words, you can restore your wallet. Just make a new wallet and choose the option to restore a wallet.

Right, so blockchain.info is probably confused now by the RBF transaction. You might have to wait a bit for it to sort everything out. You can also try contacting their support and see if they can help you.

How did you try to send it?

It is not possible to reverse the payment. The transaction is not in the blockchain. Blockchain.info simply says that it is a double spend because it is; an RBF transaction is a double spend. It's fine, the transaction has been broadcast, you just need to wait for it to confirm. What blockchain.info says does not really matter.

So you are using Bitcoin Core? If so, follow this guide for removing the transaction and resending it: http://www.achow101.com/2016/07/Bitcoin-Core-Troubleshooting#stuck-tx

Yes, there are a few miners who can do that. IIRC the user macbook-air is a mining pool manager here and you can contact him to see if he can do anything to confirm your transactions.

Your fees for the first transaction are too low. You may be able to do an RBF transaction, it depends on your wallet. What wallet do you use?

The second transaction is unconfirmed because the first transaction is unconfirmed. If you make an RBF transaction for your first transaction and it confirms, the second transaction will be invalidated and you will need to resend it but spending from the RBF transaction.

The code is right there. Just look at my earlier post. The first two code blocks are the code that you should remove from your script. The last block is what you should add right after

You can try using my fee booster software: https://bitcointalk.org/index.php?topic=1506632.0. You just need to enter the raw of the stuck transaction, follow the instructions, and it will give you an unsigned transaction. Then you sign that transaction in your wallet and broadcast it. Instructions for signing the transaction depends on the wallet you use.

The account name is probably root

You can install ubuntu again but it may not fix your problem unless you do a clean install. If you install over your current install, it may retain the issue there as settings, files, etc. are still kept.

You can't sudo under the guest account because it doesn't have permissions to use sudo.

Try hitting ctrl + alt + f1. That will take you to the TTY (a text only console, basically the terminal). Then try logging in as root there and do whatever you need to do. You can also fix the problem you are having with logging in if you can figure out the right commands to fix it; I don't know how you would do that though.

Again, you are doing it wrong, as I have been telling you. If all of the keys of the multisig address are in the same wallet, then that will work. Otherwise it will not. This is detracts from the point of multisig.

Use electrum and because using a deterministic wallet for this is better. You should not reuse addresses and a deterministic wallet makes it easier to organize and recover backups.

Theoretically it is possible. In every single Bitcoin full node there would need to be an exception coded for the block and txid of the transaction which returns the funds. Under every other circumstance, it would be considered invalid, and for anyone that is writing Bitcoin transaction validation code, it would be an annoyance to have to keep that exception there.

Sell stuff. If you have some junk lying around your house, try selling it and you can get some Bitcoin that way. One man's junk is another man's treasure.

You could also make things and try selling those.

The fiat is stored in their bank account. Usually their bank will take care of any fraud and such. The money is also usually insured. Since fiat is controlled by a central authority, then can easily reverse fraudulent transactions. Your fiat will be fine. On the other hand, with Bitcoin, you should only keep on the exchange as much as you are willing to lose.

They don't. AFAIK, typically it's one private key that is the user's that is encrypted. Then another private key is the service's private key. The last key is given to the user at account creation and that key is to be kept offline. When sending, it's done automatically. The user's browser decrypts the encrypted keys and signs. Then it passes the half-signed transaction to the server which signs it as well. Then it is broadcast to the network.

Usually they use BIP32 to generate the keys so that only three root keys are needed. Bitcoin Core doesn't do this yet, but Electrum does.

Unless all three private keys necessary to spend from the multisig address are in the wallet, then it should not be possible to send from that address. If Bitcoin Core is somehow doing that, then the transaction will be invalid.

No there is not.

IIRC HaoBTC offers interest.

It is not an rpc command but rather a startup option.

See http://www.achow101.com/2016/07/Bitcoin-Core-Troubleshooting#option-startup for help on how to start Bitcoin Core with startup options. Use the -upgradewallet option instead of whatever example I wrote in that link.