Welcome to Pet Talk!

Couple questions to help answer yours....

First... you say Nena is in heat, and you ask whether she could be pregnant. Has she been around any unaltered male cats?? If she hasn't been around any other unaltered male cats, I would have to guess no at the pregnancy thing, unless you're taking into consideration immaculate conception

The kitties, especially the 8wks old, more than likely are feeling needy and want to still feel and be mothered, and Nena is old enough and when they are in heat, many of them are very responsive to stimulation like that. I highly doubt that they are getting any milk as she would not be producing any if she's not pregnant (again, see previous paragraph on that one).

Many cats can display the nursing habits into adulthood. Depends what they focus on. Some are wool suckers, some use other materials. Many people, including vets, say it's because they were taken away from the mom cats too soon.

Get your cat spayed as soon as she is out of heat, that way you won't have to worry about her ending up "with kitten". If you need any leads for low fee spaying, let us know what general area you are from, and many of us can give you some basic info for vets and clinics etc...

Good luck!