M.: You lose a very good fight because it’s all just expenses.
What you spend is either a gift of cash in hand or a loan, but it is an expense regardless of whether you charge the project and pay cash for “elsewhere” or charge “elsewhere” and pay cash for the project. This is especially appropriate if the “other projects” are as you say, projects and not travel or paying off debt or whatever. Whether you use gift or credit in the bathroom or bedroom is a tiny haircut.
And if “elsewhere” includes more urgent things that require cash, then please don’t pressure your spouse to turn down an opportunity for better financial health just to maintain gratitude with yours. “Thanks, Mom and Dad, for helping us finish the bedroom. You’re the best,” would be true no matter what kind of money you spent where and in what order. Assuming they are actually the best.
If your parents are too tight on their gift money and that’s why you’re now pitted against your wife, making their pressure her problem, then they really aren’t the best. And you’re picking the wrong side. Instead, you should support your wife and support your parents in your right to manage your household finances as you see fit and reassure them, for the sake of appeasement if you will, that while you have other money priorities, their generous gift will push the daughter’s bedroom into line, which, again: Huge help. Thank you very much. And you must refuse the gift outright if they bother you about your honesty.
Unless your priorities stink and your daughter is in a plywood bedroom while you divert money to restore the hot tub. In this case, ask your parents to write, thank you very much. If there is financial pressure here and the whole “gift this” and “loan this” is an anxious game and your parents are genuinely trying to help and maybe their help is a bit much, then just talk to them about what is needed and they intend to they do and let’s see if they are open to it. Better to keep your emotional investment in your marriage as low-risk as possible and play with the “rents” a bit.
What you cannot do, decently, is accept the money under the guise of finishing the bedroom when you have no intention of finishing the bedroom in the near to medium future. A gift is yours, always and fully, to use as you will, but false pretenses are a coward’s courage.
Bottom line: Credit cards are more expensive and riskier money, so only charge “projects” if you have to or have the plans and means to do so strategically, to pay back promptly and with little to no interest. Otherwise, wait if you can. Michelle Singletary didn’t make me write this. If I missed an “if”, well, damn. But please let me know.