Yes, it was a little harsh and things sometimes come across a bit more so in writing. I don't know all your circumstances, only those you put in your post.
Not trying to trash you and I did not realize you could not have children for any reasons other than not enough money to support them. I did read the posts but must have missed the one where you spelled this out. I can see that this is a far different scenario.
However, if the cost of IVF (or other reproductive tech) is the only thing holding you back, what are these costs? In Ontario much is covered:
http://www.ivfcanada.com/services/fees/general_fee_schedule.cfm You could reduce some expenses, work for a year or less, and save enough for this kind of treatment - if it is something you want to do. Don't give up if this is what you really want. IMO life is too short to not give these things a shot, even if they do not work in the end, if it is worth it to you and your husband.
If you are looking to solve some financial problems, you can keep in mind that MMM and his wife worked for seven years (I think that is right?) prior to retiring. If you want to get there, you can and you have plenty of time, you just need a plan. The fact that you have a 15 and 18 year old means that some of your expenses should go down within a few years as they become self-supporting. You are also starting a business that might bring in some more funds.
I don't understand the past payments here; however, because of lack of context - which is fine. I would say though that if he was paying her $25 000 a year in child and spousal support while they had joint custody for a period of ten years after their divorce his income would have had to have been extremely high and hers extremely low to be required by law. Each party would have an obligation to pay support to the other and become self-supporting. This doesn't matter now though, water under the bridge.
You are incorrect in imo your statement "Ex is legally within her rights to enforce the issue, against her daughter's wishes, and ask us to pony up for the cost of her mortgage and lifestyle." His ex is only legally entitled to child support per the guidelines if she is the full-time caregiver. This is approximately $650 a month for the daughter if your husband makes $70,000 a year. Out of these funds, his ex would be required to pay for food, shelter, allowance, clothing and necessities of life which you now pay for.
I can understand not wanting to put the daughter in a position where she expresses her wishes, but courts tend to go with "status quo" ie. if she has been staying with you and doing well this will count for far more than you working. The ex's erratic financial circs and power cut-offs and the daughters worries would be a huge issue to her claim imo.
And yes, I'm a Canadian lawyer but, no, don't rely on my opinion in a blog, check it out for yourself further by bringing my response to another lawyer in your area as I can't possibly know all the circumstances of your situation - only those you have listed.
You are also incorrect imo that that if you work during the day and your husband travels 50% of the time your daughter would be required to live full-time with her mother. The question will be "what is in the best interests of the daughter". If she expresses a preference to stay with her dad, and you have been the primary for a period of time, the fact that you are working will not be determinative of the issue. She is 15 and presumably attends school. Children of this age can be left alone after school for a couple hours. Many many Canadian families have two working parents. Avoiding a battle about the issue might be worth it for a whole lot of other reasons, as I mentioned in my previous post.
The choice to stay at home is one that you have discussed and decided on with your husband. That is something that seems reasonable if it is what you both want. If you have a business plan that could work well in the circumstances that seems like a good idea.
As far as reducing expenses, see if your family is open to consignment/thrift shops. You can get extremely high quality items for a fraction of retail. I buy my suits via consignment and pay no more that $80 each for brand name.
Finally, have you talked with your husband about whether he could work at something locally and receive a similar wage? His wage might not be high enough to warrant the dry-cleaning costs and loss of having him in the home 50% or more of the time if there is something close by that would pay a similar amount. If he was home regularly you could work more and he could spend more time with the daughter too.