Is it appropriate to give gifts to my niece's other siblings?

My sister's daughter lives with her father, stepmom & other siblings. I have no ill feelings with my niece's family but my sis does. At holidays I try to remember their family with a gift especially the younger children (my niece is oldest). I was going to give each of the 4 kids a small bag of candy for Valentines but I remembered how mad my sis gets when I do things like this. In the past when I lived in another state I found out my family would keep all the gifts I sent & give all to my niece. I have just moved back with my family and I don't want to start any problems. But, I don't want my niece's siblings to feel left out. Is it OK for me to give them small gifts? BTW niece's father and stepmom are always very appreciative of the gifts.