I agree with posters above. Never try to own property with someone you are not married to. That doesn't go well even when it is a parent and child who co-own . . . or siblings who do it. (I've seen that with people I know very well.)

You make an excellent point, yourself, Vin. You each have young families. The "Brady Bunch" looked great on TV. I promise you that blending two sets of kids under one roof is fraught with HUGE difficulty. Your S.O. and you may love each other. That doesn't mean these kids are all going to even like each other. I betcha there would be way more friction than you can even imagine. Your first obligation is to Your Own kids. If your kids and you are living in a reasonably happy home, I'ld be real slow to disrupt that set up. Your idea about waiting till the kids are older sounded real sensible to me.

I got to wonder why your S.O. is in such a big hurry to want this huge change. Maybe it would be more financially advantageous to her than to you. If the opposite is true, that's no good either. If she sees herself as the senior partner, financially, that can become leverage that she'll use against you down the line.

I'll bet you two don't have identical parenting styles. That will lead to problems. When your kid and her kid don't get along (which will happen,) she's going to blame your kid. You're going to care more about your kids than her kids. (That's called "maternal instinct.") Your responsibility as a mother takes precedence over any relationship reponsibility to an S.O. Don't ruin your kids' lives.

Maybe this relationship with your S.O. will last. Maybe it won't. (Statistics say the odds are that it will eventually fail. I wish you luck.) But you will always be your kids' mom. Do what will best protect their interests. That will end up being what is in your best interests.

I've known some blended families. The ones I knew didn't work out too good at all. The upside was an apparent temporary increase in sexual/intimacy satisfaction. (That can seem important, and it is.) In both blended families that I knew, someone's kid ended up dead - one from a drug OD, the other as a victim of a murder. I couldn't help but wonder if those two deaths might not have happened, if each parent prioritised his/her own kids and respected their partners' obligation to do the same.