First weigh your cups of grain, nobody talks cups of grain, so it's impossible to help.
With grass hay your protein is way to low...so feed more alfalfa pellets. And stop mixing the alfalfa pellets into your grain mix. Alfalfa pellets are instead of alfalfa hay, so put them in the barn where the girls can eat on them and their grass hay, minerals and water all day long. Build up your alfalfa pellets to 3 pounds each goat per day, or free choice, moved slowly to that goal. Mine get nearly free choice (we have soo much humidity I can't actually free choice) but more like as much as they want during lactation, and they actually eat less than when they are on limited, like right now with kidding season starting tommorrow.
Then challenge feed on the milkstand. Oats is a fine base for your feeding program, just remember that when you mix your own grains together they are not then getting minerals on the milkstand, so your mineral mix becomes super important. Ask about the 18% sweet feed, what percentage is molassas? Anything over 10 and pass, or...you might want to buy it and mix it half and half with your clean whole oats, but do aim to get the molassas down into the 6 or 7%. Molassas defeats the whole purpose of challeng feeding because it builds up so much acid in the rumen the girls eat less. You then have to feed yeasts and bicarb to make them eat more and calm the ph of their rumen
Start with your cups you usually feed, converted to pounds...so if your two cups is 1/2 a pound, than the day they kid they get 1/2 a pound of your grain mix (minus the alfalfa pellets because they are in the barn) morning and night. Weigh your milk once a week, I do Monday mornings. Then Tuesday up the grain amount by 1/4 a pound morning and night....weigh the milk the next monday...did they increase the amount of milk? Than increase the grain by 1/4 a cup morning and night on Tuesday....continue. When you weigh the milk on Monday usually around week 4 if they are no longer making more milk than the previous week, they have met the challenge for them so decrease the grain back to the 1/4 pound increment from the week before before.
Allthough a really good milker may be eating 2 or 3 pounds morning and night, others will only be eating 1 or 2 pounds morning and night, and sadly others only 1/2 to 1 pound morning and night (because of poor milk amounts). You also don't want to start a doe out as soon as she kids eating 2 or 3 pounds morning and night because it will increase their milk way to fast and it can also throw them into milk fever. You have about 4 weeks to set their lactation like this.
Remember your alfalfa pellets, hay/browse, minerals and water are a constant in the barn.
Then I weigh milk each Monday....if they start a decline in milk, which you expect a plateau at about 12 weeks, and hopefully only a slow steady decline...here we have dismal milk in August, during which time they deplete in milk, or increase again in september I juggle the amount of grain they get.
3 of my best milkers milk very well (12 to 16 pounds) and stay in way too good of flesh on alot less grain than most of my other does, and it's why I am concentrating my genes into this part of my bloodline. You would never know this without challenge feeding and weighing your milk.
Hope this helps, course I am one of those OCD folks

Vicki