Depending on the currency, a Revolut or TransferWise sending account will be in your name as the account holder, even though it might be a non-bank and/or E-money account.
On the other hand, transfers from a third-party account to a brokerage account are not a good idea in my opinion.
No reason to do so - unless you want to try to “obfuscate” the origin / source of these funds?
If you have an account with IBKR UK, you should be able to transfer EUR to IBKR directly - as an inexpensive/free SEPA transfer.
How much? It shouldn’t be much if coming from your parents, should it?
Also, you might want to check whether any and which amounts are exempt.
No.
Transfers between your own accounts are not taxable, whereever they may be located. Of course you did already include these foreign accounts in last year’s tax return, didn’t you?