For your mom, she doesn't need to agree with you on it... she just needs to know not to force retract his foreskin during diaper changes or bathtime but to only allow the owner of the penis to do that (your possible future son)
For your husband, the arguments you use will depend on why he is for circ. Is he afraid of locker room teasing? Is he struggling with you wanting to keep your son intact while he is circ'd and hearing it as 'your penis is bad, our son's will be good.' ? Does he just like going with the status quo without ever questioning why? Is he worried about your (possible future) son needing one as an adult and it hurting 'worse' and not understanding that it hurts just as much as an infant only they can't say so... and also pee and poop into the cut without having the same medications as an adult would have to help block the pain?
Ultimately, your (possible future) son DOES deserve an opinion. You can always get a circumsicion later but undoing a circ is extremely difficult (some say you can't undo it but there are a few men out there who have had success with what basically amounts to weights on the penis for very long periods of time... most men will probably not be willing to do this and from what I understand, it doesn't work for everyone anyway.)
Forget about your mom's opinion, just focus on getting to the root cause with your husband. At worst, you can always use the argument that the discussion of whether or not you should circumsize should come up at a later date post birth because doing it right at birth can mess up the breastfeeding relationship, even make it impossible because of the pain and confusion the newborn will experience. that and no one dies from not getting circ'd but babies die every year from it. Waiting til later raises the chances of not dying because blood will clot better. AT 3-6 months, he might not even bring it up again because he has grown used to seeing an intact penis and caring for it (which is easy.. you just wipe it off like a finger and do nothing else) that it doesn't matter that you never circ'd. If he does bring it up, you'll have an easier chance at asking why he wants to do it when there have been no problems so far. You just have to make sure you word the original agreement as having the discussion again... not making him think it WILL happen at a later date.