It's Tanvi50_. So technically it's not mine, but I do have access to it. I have taken some of the merits in the past from that account, and I will say this again. I didn't know back then that how merits works. And other submission were getting a lot of merits, so I thought I can get some from my sister's account. So I did. The amount is 28, but I did also give merits to other people too. You can check my merit history. Someone I know personally, I shared it with him, and he said it was against the rules of Forum. So after that I stopped doing it and only gave out merits to who deserved it.
First of all abusing with the merits won't get you a ban and moderators have nothing to do with the merit abuse and DT community decides whether you can be trusted after doing such a thing with their ratings.
Technically you circulated the merits between yourself either its from your own account or your sister's as per your story but you did on yourself which is not really encouraged again this won't get you a ban but you're at the risk of getting negged.
And for the next part, you can merit any post you want as long as you're doing it from your own sMerits, like if you simply like a post or even a post with one word received tons so it all depends on the adding meaning to the discussion in some part.