Hi again, and thanks for your additional information about your mom-cat to be!
A cat's gestational period is approximately 9 weeks, so she's not quite ready, unless you've miscalculated. Slowing down in activity is not abnormal, as she's more tired as she grows bigger, however, if you notice such a big change in her activity level at this time, it would be a good idea to have her evaluated by the vet to make sure all is well. She may have some nutritional deficiencies, as the kittens are 'taking' from her, too. Is she eating a premium KITTEN food? This is recommended for pregnant and nursing cats, to supply extra calories and nutrition. The vet may also suggest some nutritional supplements and vitamins.
About 24 hrs. before labor begins, she would become restless, searching for a good nesting place to give birth--prepare a nesting box for her, in a quiet, dimly lit, non-drafty area, and show it to her now, so she might start sleeping there and get used to it--you can put one of your unwashed t-shirts in the box so your scent is near her and makes her feel secure. She will also slow down in her eating or have no appetite at all for 24 hrs. before labor begins, so if she's eating and drinking a lot now, she's not ready to give birth.
The following will provide you with some helpful information re: feline pregnancy and delivery:
It will be important to keep the Tom cat separated from her and the kittens when she gives birth and right afterwards. She can go into heat as early as 2 days after delivery (this is rare, but can happen) and the male will do anything to get to a female in heat, including hurting or killing (unintentionally) the kittens. If she and your Tom are close, SHE can visit with him (as long as she's not in heat), but keep the kittens and her nesting box in a separate room.
Having your Tom neutered at this time (I assumed he's not?) would be a good idea. However, the mom-cat and kittens should still be kept separated from him at first.
I hope all goes well!