Potty Training: An Almost-Three-Year-Old and His One-Year-Old Sidekick

Big Boy has decided he is ready to wear Big Boy undies and go potty in the potty.
So we got out the undies we'd bought a couple months ago.
First issue: These are mommy undies, not daddy undies. These have short holes, not long holes (translation: these are briefs, not boxer briefs like daddy's). So I showed Big Boy how there's a little flap in the front of his, just like in daddy's so he can go potty without taking off his undies.
Second issue: He can't open the flap on his own. There is a lot of digging going on. MrDartt suggests that Big Boy just pull down the front of his undies ("That's what I do," he says.) Big Boy refuses. Maybe that will be too much like what mommy does. So I have to help Big Boy open the flap and get his pee pee out. This makes me very uncomfortable because you really have to get in there, and it seems very physically uncomfortable for him.
Third issue: While I am distracted with the flap-opening situation, Little Boy is madly crawling for the potty, and before I can stop him (because I'm determined to give Big Boy the right amount of attention during this whole potty-training thing), he's splashing in the toilet. Really. So Big Boy says, "Going toilet-diving, Little Boy?"
Fourth issue: Once the pee pee is out and Big Boy is peeing, he's forced to hold it pretty close to the end because of how the flap sits. So he gets pee on his hand EVERY time. So he has to wipe off his hand and his pee pee with toilet paper after he's done.
Fifth issue: Big Boy either spends the entire day in the bathroom, trying to go potty over and over again (but of course, most of the time there isn't anything there because he's in there literally every three minutes), or he refuses to go, and then suddenly it becomes very urgent because a tiny little bit of pee has come out.
Sixth issue: Sometimes not all the pee comes out the first time. So then Big Boy has his undies and pants pulled up after he's gone potty and then a little more pee comes out. So we're taking Auntie Laurel's suggestion and telling him to pretend he's a firefighter: the pee pee is the hose, the pee is the water and the toilet has a fire in it. Squirt 'til you can't squirt no more. Put out that fire. Seems to be working.
Seventh issue: Pooping. Big Boy held his poop the entire first day. But yesterday while we were eating lunch, he jumped off his barstool and ran to the back of the house (he insists on using the potty in mine and MrDartt's bathroom). I said, "You're going potty again?" He yelled, "I have to poop!" Sure enough, by the time I got back there, he'd pooped in the potty! Ah, a major success. He got mommy cheering, jumping up and down and yelling, plus ice cream for that one.
Eighth issue: We don't have enough undies. We have three pair. Yesterday he had three pee accidents right in a row! We were out of undies! So we have to buy more today. And I'll be looking for boxer briefs like daddy's.
There's just so much to think about, but I LOVED not changing a poopy diaper yesterday. Because Big Boy poopy diapers are BIG BOY poopy diapers. And I admit, this is kind of fun!