1500!? Come on! Thats less than someone who's cutting:P
Start using a calorie counter app, myfitnesspal is my recommendation, keeping track is a must because you will have no idea if your over or under unless you count! You may think you have enough but will realize your way off.
As far as jumping from 1500 to 3000? Nope it'll take you a few days or a week or so to adjust.
I'd endorse milk if I could! Quick calories and PROTEIN! I'm up to 7-10 glasses a day usually. You gotta ease into it, but after a week, all that milk will feel like nothing. Spread it out, one glass every so often, every meal must include milk!
8 cups = 1040 calories, 72g of protein.
Of course you may have alternative ways of getting your calories besides milk but its one of my favourites, I assure you you'll start loving the taste.
And as far as your cousin, anything work for him?