RENT that will save you another major meltdown when your roof needs repair, new water heater, etc.
As for your siblings, let it roll off your shoulders. Rivalry runs deeps and its really nothing personal. Maybe they want you to fail so that you'll come home and see them more often

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Kindergarten will be great. The first few days might be rough, but then after that you'll be amazed at your little one. Mine just moved into preschool at 2 (!) and he is doing fabulous! I can't even believe the things they are teaching him so young (drawing straight lines, etc).