NO....... they WILL breed whilst she is nursing, they mate again within 24 hours after birth. She will delay implantation of the 2nd litter for a week or 2 having them 4-5 weeks after the first litter. Yes the male does help in keeping them warm but the last thing needed here is gerbil multiplication every 4 weeks.

Also as they have been apart for a while now putting them back together may result in fighting between Jade and Sage.

Finally you have to be very careful about breeding a female who lives with another female - the one bred from must be the dominant female else she will stop the subrodinate from tending the pups (and they will die). So it is as has been said ok to leave a pregnant female with a female pup of hers to help raise the next litter. TM - do NOT get another female to put in with Sage - there will almost certainly be fighting and the babies may get killed - Sage will not accept another female whilst she has pups to defend as well as territory. If she were living wit

Gerbil mums do "do their own thing" as usual often appearing a little neglectful. As long as when she sleeps she is in the nest with them and feeds them regularly then I would say (without seeing them) that it sounds normal.

As for the death/sickness - Sage wasn't in the best of health herself, the genetics and health history are anyones guess so it may just be that these parents produce sickly pups - so again another reason to keep them apart so they do not breed again.

The last thing Sage needs is to be pregnant again.