I feel like a chicken murdered!

We decided a while ago, it would be great to get some chickens. expecting them to be fairly low maintenance, and good from a sustainability point of view. We got out first 2 in August 2012 and seem to have managed to kill 5 of them since. is this normal?

The first two we got, (Salmon Faverolles) one died after the second night. It had a weird ball patch on it's bum, so maybe wasn't 100% healthy, but main problem with that one is that teh bulb in teh heat lamp went out in teh night, so i guess it got cold, although it did survive another couple of nights.

When we got a replacement for her, we also got a third one (one Salmon Faverolle and one Pekin Bantam). One faverolle got sick just before Christmas, we took her to the vet (who thought she had gastro), she finished her course of antibiotics and died the next day (boxing day), she was about 22 weeks old.

The next faverolle went the same way about a month later although she died on the second day of antibiotics, even though she looked a lot better that the first one who died. She got an autopsie and turns out she got some sort of stomach infection, which we apparently couldn't have done anything about.

The pekin Bantam was then left on her own and got very broody, so we discussed with the breeder and decided to get her day old chicks, we got 2 polish, 1 peking bantam, 1 wyandotte and one autralorp. The mum adopted the other pekin pretty quick but it took a bit lonegr for the others. About 2 days after she adopted them all, i found the peking dead. Now 3 weeks later, we come back home to find the Wyandotte lying in the coop on her back on her own, but still breathing. Took her inside, put a light over her and tried to feed her a honey and water mixtur. She lasted about 30 minutes before she was dead...

I think we look after them well, and I really don't know what else we can do, but it seems like a lot of deaths in only 8 months. Is this normal at all? Any help greatly apreaciated, it's really put me off getting anymore!

 

They are on chick starter feed, they have apple cider vinegar in one water container and garlic in the other. They have a purpose built coop where they are well protected. the coop came with a run which we have extended. The bedding is kept dry and regularly cleaned. They stay relatively close to their adoptive mum and run around full of energy. They don't have a heat lamp as i was told that would likely make them go away from mum instead of going to her for heat and anyway, it doesn't really get very cold at night at the moment (in Perth, Australia).
I've followed all the advice from the girl we buy them from, who has years of experience and also taken them to the vet as soon as i have seen the slightest sign they may not be well. the vet is sure theer is no disease / bacteria lingering in teh area or they would have died within shorter periods.
I was wary of going for really young ones, but givn we had a broody chook, it seemed like the best solution, and she has adopted them.
From everything i've been told and read, it seems we are doing it all right and are just very unlucky, but I can't help feeling really bad. Anyway, thanks very much for the advice and hopefully this is the last of the bad luck!

 

Thanks for all the responses, i guess i will just have to accept it's bad luck.
I don't think there are any issues in the breeding or husbandry practices as she is a well respcted breeder and educator, also the two faverolles that died had got to 22 and 27 weeks and were very healthy seeming and laying eggs which i believ they don't do if unhappy or unhealthy. Hopefully the mum and 3 chicks we have left make it