I have an important question about importing wallets from either trust wallets to blue wallets or trust wallets to Electrum.

Reading through posts about the best Bitcoin wallet to use here in this forum, I happened to understand that TrustWallet is not in any way recommended as it is not open source, so now I decided to use my old wallet created using the TrustWallet multiwallet option, which accepts both bitcoin and other altcoins (that apart). I used the generated phrase to import it into my blue wallet and that of electrum on my mobile device.
 
Upon doing this, the blue wallet gave me a new bitcoin address, which I can start using for receiving new incoming transactions. My old balance on my old wallet is still visible with the blue wallet, but when I click on the receive option, I see a total different address, and on the address icon inside the blue wallet, I notice that I still have about 20 unused addresses, and my imported address has been marked as used.

Here comes the question:
1. If I happen to use any of the generated addresses from BlueWallet that are attached to my phrase, can I spend them using my trust wallet? Since I can still spend anything from my old address using a blue wallet or even my electrum, trust wallet allows me to do the same thing, as I can't fine any of such options on trust wallet.
2. Among the new addresses that were generated, if I happen to receive new coins into them and I want to spend just the coin I received with the new address, leaving the old one that came with it when I imported the address, will it be possible for me to specify which address I want to be debited from? And if yes, will my transactions also be linked to my old bitcoin address, which I have been using in the past?
 
These are just questions running through my head out of curiosity.