I hear your concern that you aren't making enough milk. Babies go through growth spurts at 3, 6, 12 weeks and 6, 9 and 12 months. (give or take a week or month respectively) It will feel like the baby wants to do nothing but nurse around the clock for about three days or so and then will go back to the usual routine for the most part. Breastmilk supply works on demand, so the more the baby is demanding, the more you will make. See if you can get your husband to let you take a breastfeeding weekend where you stay put with the baby and he takes care of the toddler and the housework so you don't have so much to take care of and can focus on breastfeeding on demand. Also, don't judge what your supply by what you produce with a pump. Many women who can't express a single drop are able to breastfeed fat healthy babies from the tap, so to speak. Not everyone responds to the pump, and that's OK. What counts is the baby's ability to get milk. You can gague that by counting wet and dirty diapers. She should be having 6-8 wet diapers and at at least two stools a day. At this point if she goes for a few days without stooling, be on the lookout for a big blowout. To increase your water intake, when you go to get that glass of water to sit down with, gulp it down and refill your cup before sitting. This will maximize the amount of water you get each day and if you only sip on the glass, get distracted by your toddler or your mom has an urgent need, you will already have had one glass already. As far as supplements go, try eating oatmeal. It can be hot cereal, cookies, in granola, etc. The steel cut hot cereal is best, but instant will work too.
It sounds like you really have your hands full with two babies and your mom. Just go with the flow. Feed on demand, drink plenty of fluids (water, milk, juice), and have faith in yourself that you can do this.