Your babies are not new toys that everyone in the house gets a turn with.
They need you, their mother. They need you more than they need their dad, and certainly more than they need these very weird grandparents.
Reach out to your HV and to your GP. Contact the doctor who cared for you and the babies in the hospital, and any midwives who cared for you.
This situation is completely untenable, and you are at risk of developing PND because of the bullying you are being subjected to by your husband and his parents.
You need the support of people who are sane and caring and who have your best interests uppermost. Your husband does not, and his parents do not. Your husband is only interested in facilitating his parents' abuse of you, showing off the babies to them and edging you out because he hasn't succeeded in cutting the apron strings and wants the approval of his mummy more than yours.
Living with the grandparents while saving for a home of your own is turning out to be a very bad idea. Please call your council and see if you can be placed on a housing list ASAP.
Even if you end up taking the babies into the bathroom with you when you use the loo, you need to stop the baby snatching that is going on, and you need to stand up to the verbal abuse your husband is heaping on you when you object.
Do you have parents of your own? Any family at all? Friends? You need to reach out to anyone outside of the house you are living in and ask for their moral support and if possible, a room to live in with the babies.