If you write
I asked about that yesterday because I have been getting weird emails.
have been getting implies that you got them in the past and continue to get them today, when you are writing. Obviously, it does not imply that you will continue to get them in the future. It is silent on that point.
If you write
I asked about that yesterday because I had been getting weird emails.
had been getting implies that you got them in the past and continued to get them up to the point yesterday when you asked. It does not imply that you continued to get them after that point—today, for instance. It is silent on that point.
?If you asked him to do the chores, he should be doing them right now, since he had/has decided to help you out more.
This is a complicated and, frankly, awkward sentence. In the first place, if and decided feel wrong to me: if seems to question your interlocutor's account, and surely you should be talking about promises, not decisions?
In the second place, your three clauses create odd tensual shifts. This is ordinary in conversation, where you speak off the top of the head, improvising from point to point; but in conversation your hearer knows the context, so you don't have to worry about making the tenses coherent.
So I'm going to ignore the first clause, and change decided to promised:
He should be doing the chores right now, since he ?has/ ✲had promised to help you out more.
In this context, you cannot use the past perfect because there is no Reference Time to which it can be related, no past time which it happened before. You may use the present perfect; it's perfectly correct; but there's no reason why you need to. Promises (and decisions, too, for that matter) are inchoative, they mark the beginning of a continuing state, so the idea of continuing into the present is as it were 'built in' to the word itself. A present perfect doesn't add anything.
Consequently, the natural way to say this is with the simple past:
He should be doing the chores right now, since he promised to help you out more.
✲ marks an utterance as unacceptable
? marks an utterance as possibly unacceptable