Perhaps, somewhat selfish, but that's not always a bad thing. Apparently you were both married at the time of your second child's conception, so that was a choice that you both knew would limit your money and personal time. Having two kids close together is harder on a woman's body, so the weight loss might be a bigger stumbling block than if there was just one, and also her energy after dealing with two kids all day will be understandably lowered. The facts remain, you are where you are, and while fantasies of an easier simpler life seem to be rearing their heads, you must remember that this was what you chose, remembering that might help to lessen the feelings of being stuck.
Naturally, her career goals are on hold. Going to school with two kids not in school yet would be extremely difficult for both of you, you think you're feeling pressure now! I don't have any easy answers for you because I find the early years of raising kids to be the most difficult. It will get easier once they are in school, and perhaps your wife can resume her schedule then.
You, however, won't last another four years at this rate unless you find some way to divert your attention away from the frustration you feel and into something more positive. Selling your bikes, that sure does blow, but I'm sure that many if not most of the young fathers on here will relate similar stories. My son-in-law that I spoke of earlier had dirtbikes, and it's just one of those things that you do to benefit your family when you make the decision to have one. You're no longer just a guy with some hobbies, your family being one of them. Now you're a head of household, like it or not, with more responsibilities than free time. Yes, it's tough. I didn't make it myself, so I'm not preaching. My own husband was so jealous of the time I spent with out daughter, he became something of a hypochondriac demanding constant sympathy. He just didn't understand why I couldn't work all day and come home to take care of our child AND pay him huge amounts of attention over every little sniffle he had. What I wanted was some help from a fellow adult, and some sex now and then! I didn't need an adult child to take care of. It sounds like your wife's interest in sex is not very strong, and that may be a bigger problem for the two of you than anything else. A woman's weight is often a reflection (to some extent) of how she feels about herself and her sexuality. Most of us know that men find us more attractive when we're a certain size, and (I'm going out on a limb here, but speaking from personal experience) sometimes the weight is a way of keeping men at a distance, if even subconsciously. She's got two kids at twenty-four, she's tired, she doesn't want to have to perform anymore, maybe she feels that taking care of your kids should endear her to you enough without having to add another struggle to her life to lose weight. I'm guessing, of course.
Honestly, child care being as expensive as it is, have you seriously considered if she could reasonably earn enough to make a positive difference in your families' cash flow? I don't know what her education level is, but more hours for her might not mean more in your pockets at the end of the week if you have to spend a lot on child care. However, it may give her a break and get her more into the adult world and perhaps that would benefit her outlook, I don't know.
I hope you will consider well the ramifications of straying. I think you would not have posted if you weren't looking for some sincere advice. If your marriage is assumed monogamous (which most are), then it would be dishonest of you to have an affair behind your wife's back. In addition to crushing her if she found out, it might have adverse affects on you as well. You won't know until you get there, but most people are not so hardened that they can break their promises and still feel okay about themselves, and what if you DO teach yourself to do this? Is that really a talent you want to learn?
Man, life is hard! I wish you the best in your search for what road to take, post often and let us know how you are doing. I appreciate the candor with which you've spoken about your personal life, perhaps talking like this with her would be of benefit, if you think she could handle it. Much love, Jana