1. Yes, since transfer of 5 lacs in your a/c is documented.
2. For now, after returning them all the stridhan, you can ask them to sign an undertaking furnishing that they have already received all the receivables and they will not claim the same from you in future.
3. they can, because the mutual consent divorce terms are still not finalised. Better that you strike a final deal with them so that you avoid the risk of facing their unreasonable demands now and then in lieu of divorce.
4. If they are ready for MCD, you should get it specifically in the consent terms that they will not file any case against you in future, including 406 and 498a.
5. No, not advisable. Instead of entering into this agreement, finalise the consent terms of the the MCD only.