Hi Straydum,
Thanks for the quick reply.

okay first of, angels cohibiting in odd numbers generally do not do as well as those kept in even numbers. from what you wrote, it seems that previously, your smaller pair has sort of paired up (correct me if i;m wrong), if so, then does your bigger angel still pick on them like how it does now?

I thought I read somewhere mentioned odd number is better than even number. Of course if there is a pair, then their own tank would be best. Or maybe they were talking about Discus, I don't remember.
Anyway, like I mentioned, one small one found dead few months ago so now I only have 1 big one and 1 small one. And I know the best way to go about getting compatible pair would be get 6~8 juvi Angels and grow them out and let them pair up. However, when I got them these 3. I got them from another local aquarium society member, and he just sold those 3 in the bag. And I know the 1 was bigger from the start. It was 2 quarter size and 1 half dollar size. It was back in January. They were fine until April. I found 1 of the small one dead in the morning. I didn't see any so called pair up behaviour or aggression toward the small one died.
Like I mentioned, the big one have been peck at the other smaller Angels but it was more of the motion of peck and I don't think I see actually s/he peck at the smaller Angels. Before s/he would peck, the small one swim away a bit and avoid the pecking. After the one small one gone, it is still same. Now and then the bigger one do the motion of pecking but the small one avoid. And it doesn't happen often. Only the time I notice is after I do the water change and big one do more pecking motion when the small one come near him/her. But I thought this is because of the re-establishment of territory. And I never see any aggressive chasing or body bruse or torn fin or anything like that.

if it didnt, it was probably due to the fact that the 2 smaller ones were less vulnerable as a pair. this however no longer stands. the recent peckings, though not severe now, may intensify. at the same time, it puts real amounts of stress on your smaller one so i suggest you watch them carefully.

The degree of pecking haven't changed. Either when I had 2 small one or 1 small one now. I know that 2 is not good to keep if they are not a pair since one is always dominant than the other one. That is why keeping bigger group and pair them up and rehome the rest is good way to go. So any aggression would be spread around. But I never had chance to add more to the original 3 Angels. And I lost one small one in April and I wasn't sure if it is a good idea to add more Angels and what size. But I did keep close eyes on them but the degree of aggression have not changed. But my concern is small one seems not growing much if any. Despite the fact that I see him/her eat his/her share of food.

regarding the not growing part, what are you feeding them? and anymore info you can supply?

I feed mainly flake food since I tried other pellet but they didn't want to eat. I also give occational live food.( I know it is always the debate of the pros and cons of feeding live food) But they do enjoy occational white worms, daphnias and bloodworms. Beside I worry about if they haven't got enough nutrition. I feed flakes twice morning and evening. And I feed the mentioned live food 2~3 times a week few hours after the morning feed. I keep them in 20H ATM with 2 small bristlenose pl*co. And ph is around 7 and around 80F. I don't know about GH since I do not have test for it. I do 50 % water change weekly or sooner. The tank is planted heavy enough there are many hiding spot that I cannot always see them. But I can see both of them when the time to feed. Both of them come near the surface to get food.
Anyway, bigger one is fine s/he has grown since January but the small one just not seems to grow much although s/he have been eating. And wondering if it is some parasitic worm is the cause for this. And what is the best medication avairable in U.S. And is it worth buying and trying the so called medicated food. Thanks for the help.