could, telling, was

[jiang]

Dear teachers,

I have three questions to ask:

No.1
I will be obliged if you could help me.
Could you please explain if this "if you could help me" subjunctive mood?

No.2
I ____ them that I think they are making a great mistake.
a. will b. am telling
The key is 'a'. But I think 'b' is also possible because we have "they are making". Is that right?

No.3
I should very much like to go to the party but_______.
a. I have not been invited b. I was not invited
The key is 'a'. But I think 'b' is also possible. Or if it is the sentence should be "I should have very much like to go to the party but I was not invited" which suggest something happened in the past?

Looking forward to hearing from you.
Thank you in advance.

Jiang

[Soup]

No.1
It's a polite request using conditional-if.

No.2
I am telling them that ...
=> It's possible not because of parallel BE + making, but, rather, because it expresses present progressive; e.g.,:

Sam: (interrupting Pat who is speaking to a group of people) What are you saying to them in French?
Pat: I'm telling them that ... .

No.3
I should very much like to go to the party but_______.

a. I have not been invited Standard English
b. I was not invited USA variant

Note, the present perfect is merging to the simple past in American English.