Actually, #1, #2 and #3 can all be for financial reasons, if the reasons are severe enough. If one spouse is habitually being gravely irresponsible with the family finances, so that the couple will not have the means for present and/or future self-care, children won't be cared for, or so that the responsible spouse will have nothing to leave to adult children, that is grounds for a legal separation of finances. The couple is still married in the eyes of the Church, but the reckless spouse is legally prevented from touching the finances held by the responsible one for the good of the family. In other words, the responsible spouse is not morally bound to remain legally married while the reckless spouse ruins the family business or causes the family home, farm or estates to be sold to pay debts.
For instance, if I were able to keep us as a couple on financially sound footing by legally separating our finances, I could get a legal divorce from my husband, if he was choosing to go through our money like water, even if we as a couple had no children to protect, if my reason was so that neither of us will be eating dog food or even living unjustly on the public dole in old age. I wouldn't have cause to do it if I just didn't like the way my spouse handled our disposable income, but if this spouse were going through all the disposable income and beyond that, then divorce for preservation of our material welfare would be a morally sound choice. We would still be married in the eyes of the Church, and neither of us would be free to remarry. (I'm assuing the financial issue did not reflect a fundamental and irreparable flaw in the husband that was present at the time of our marriage and was truly incompatible with his ability to be in a sound marriage. In that case, a decree of nullity would justly free me to attempt marriage with someone else.) Even if our marriage is valid, I have the moral right to save our finances, whether he likes it or not. After all, I promised to take him for worse, but he also promised to take me for better!
As for #3, it is just saying that preserving the financial welfare of adult children and extended family are morally sound reasons for civil divorce. This does not include preserving finances from the legitimate expenses of old age. It is not OK to falsely impoverish one spouse in order to use public programs intended only for the truly destitute so that a person with solvent finances can preserve the family fortune.
If local laws allow a legal separation to accomplish these serious objectives without civil divorce, however, then that should be used, and not civil divorce. That depends on the legal jurisdiction and the particular case....that is what "if it is the only possible way" means.