This actually sounds pretty normal. Kittens are like kids - they don't know enought o be afraid of what they don't know! And, being felines, they are CURIOUS, so they head over to investigate!

Since they are siblings, they are used to being rampbuctios together, and they just egg each other on. Daisy hasn't been around young ones in a while and is uncertain what they are.

Keep are water squirt bottle handy for the next 2 or 3 weeks. Anytime you see Daisy advancing threateningly towards a kitten, warn her verbally and then squirt her. Command should always be her name first, then the command. "Daisy, NO!" "Daisy, LEAVE IT!" She will learn to heed your verbal warning and then you can issue the command without the water. It will take 2 to 3 weeks for her to accept them in HER home. (May even be longer than that, but I doubt it.) Don't leave her and the kittens alone together until you are sure they can co-exist happily. When everyone is out at work and school, leave the kittens in a bedroom with litter box and water, and Daisy in the house. Next day, Daisy in the bedroom, kittens in whatever part of the house you have kitten proofed!

Gpood luck and keep a camera handy for all the fun ahead of you!