Well I have a few questions for you...and them.
The first one is, like another asked, do you want a job and if so, what kind? FT, PT, WFH, etc?
The next is what kind of job does your husband want you to get? OR, is it his parents pushing him to push you to get a job???
The only way your inlaws should have anything to say about it is if they are helping you financially...or, if they will provide daycare either if they are able to take care of the boys themselves, or pay for it. Do they have any idea how much daycare costs? Depending on if it's home or center-based, for those three boys it can range from $300-600+ per WEEK!
Will you be able to find a job that will cover those expenses and make it worth being away from your boys?
If you find a job opposite your husband's schedule, so he's taking care of them while you are at work, that may be an option, but it's still very difficult to do. Will it be worth the extra income (if any after daycare, gas, and other work-related expenses) to not kiss the angels goodnight or see them when they wake up anymore? And what about the reduced time for you and your husband?
There is SO much more to the question of to get a job or not, and it seems that with the pressure they are putting on you, they haven't really thought about it...
Bottom line is you need to do for you and your boys...your hubby's parents can take care of themselves.