Hi Ashley! Wow Germany! I don’t think we’ve had anyone on the board that is living there. Welcome!
I am really puzzled about the notion that you were informed by the pet store that you "have to breed them once." You are spot on that it’s false information, in fact it’s a cartload of fertilizer. Female buns have an 85% chance of getting uterine cancer and my land, you can have two boys or two girls but it is often harder to bond them. It is rather interesting to hear about cross-cultural notions of animals.
The vitamin drops are unnescessary so long as they get a balanced diet, the salt lick and the chalky bar thing (I’m guessing is a mineral or limestone block) a definate no, bunnies get all the vitamins and minerals they need from pellets, hay and veggies, not to mention it makes them very thirsty. I am also thinking those vitamin drops are not very tasty for your bunnies.
Hay is great 24/7 they need to keep their gut moving and need to forage constantly. Is it alfalfa or timothy hay? Unlimited pellets shoudl be offered to them from six weeks until adulthood, for your spot (Is it a dwarf?) should mature around 12-15 months and your dwarf lionhead around 9 months of age. There is some great info here on diet for young ones through adulthood here:
http://www.rabbit.org/faq/sections/diet.html
Binky Bunny provides a great visual with adult diets here too:
https://binkybunny.com/Default.aspx?tabid=60
Veggies should wait until 8 weeks of age (your two qualify, again mystified with the six months), start with one veggie at a time, start with simple and gentle ones like parsely, kale and carrots to see if there is any adverse reaction if not, add another. One thing about the unlimited pellets, if your bunnies seem to be getting too tubby, you may need to switch to less pellets, and l imit the amount of alfalfa hay. Have you found a rabbit vet to perform the surgeries?
Are you housing them seperately? Males mature as soon as 3 months old. As for when they can be altered, most vets will wait around 4 months for females and males around 5 months old although it can be done at 3 1/2 months or when the testicles descend.
Here is info on finding the right vet;
http://www.rabbit.org/faq/sections/vet.html
Altering your bunnies;
http://www.rabbit.org/health/spay.html#age
A lot of info is available here on Binky Bunny under Bunny Info and another good place to look is http://www.rabbit.org. Of course ask away here too, we’ll be glad to help! It can be overwhelming to look for info on the web so don’t be shy! We’ve got lots of info stashed away in our heads!