1) In a deterministic wallet can somebody guess all the private keys from the wallet if one of them is compromised (if the one compromized is not the seed key but lets say the 2nd one)?
No, however, if the MPK and one private key is compromised, then all of the private keys can be computed.
The master key can only be compromized if somebody hacks into your wallet physically.
However a random private key could be guessed if the signing process is flawed, so i wasnt concerned about the master key, but rather of the individual keys of addresses.
A deterministic wallet is not necessarily a physical device, like a Trezor, so your first statement can't possibly be correct.
If one of those "random private keys" is guessed/leaked,
and the attacker also has your master public key (i.e. the thing to generate the list of addresses, but not spend from them), then he has something just as good as (if not equal to) your master key: the ability to know your private keys.
What if none of my addresses in 1 wallet have cross-transaction between them, and they are all receiving payments from different sources, then is it posssible to reveal privacy & identity here or link together those addresses (they are all deterministic of course)?
No, privacy should be secure here (at least until you spend, and combine inputs): there's nothing obvious that links one address to another, just because they come from the same deterministic wallet.
What is a HD wallet?
HD = Hierarchical Deterministic.
https://github.com/bitcoin/bips/blob/master/bip-0032.mediawiki has details on it, but basically it means that you can have one master key create more deterministic wallets. Not all deterministic wallets are HD wallets, but I think the terms are sometimes used interchangeably anyway.
