Eliakumuslam wrwb,
In this situation do the following:
1- Write them the number of the expired passport also tell them that it is expired on that date and you have applied for the new one.
2- Tell them your File number with the case processing centre.
3- Use some other ID number as well which is not expired for example CNIC.
4- When your husband will go for his medical he should bring his Old passport with the new passport as well, also take the CNIC PLUS the letter from visa office and letter from New Delhi.
5- For New Delhi documents mentioned from 1 to 3 will be more than enough.
Wish you good luck.
Thank you