Why are you so hell bent on tying yourself up legally with this man?  You stated you wanted to be married but now are twisting every little thing in your head to make this work when your gut says danger.  

There is nothing wrong with dating this man for YEARS.  In this day and age you can even have sex with him and not be judged harshly for it.   

The one thing that people forget or don't know is that divorce is devastating on your finances.  

Even living in the same building you will have opened yourself up to be harrassed by SDs.  

Just keep in mind that no matter what you come up with as to making two homes into basically one living space, that at some unexpected (but very sudden) unfortunate event occurs, these three females may end up with Dad 24/7 365.

BM could drop dead, be in a incapacitating accident, be hauled off to the loony bin, become a unfit druggie. It happens.

The little six year old is with her father now for at least the next 12 years .... long after your two daughters will be grown and out of your side of the 'home'.  

Yes, people live separately and still manage to make a marriage work. Sometimes it turns out, sometimes not. But currently you're expecting this man to be only tied up with his daughters every other week (15 of 30 days a month). Are you prepared to be a realist and also factor in at some point it may be you and your girls on one side w/him and his girls on the other 30 days a month? Then you on one side with your girls gone (grown and out) and him and his last littlest girl on the other side anywhere from 15 to 30 days a month for the remaining of the 12 years?

Are you prepared to schedule adult get-aways around only his available kidless time as your kids grow and leave and his are still there. Or will that be the new resentment that doesn't work for you. 

Do his finances allow him to be totally self reliant on his side of the double dwelling Or will he need assistance in making all his bills an child responsibility. A duplex or side by side condo usually means two complete household bills/expenses. Double this and double that. 

What about any chance of either one of you being transferred with your employment? One temporarily unexpectedly unemployed. What happens to the living arrangement and financial needs of two homes then? 

You've know this guy less than a year and lived with him approx. one month, if I read correctly. 

Is there really a huge need to immediately jump into getting married and being under one roof. Would it make more sense to go back to 'dating' a while and see if any other problems and issues pop up? 

Usually one side of a couple wants to get married more than the other. Which one are you? Is he pushing you to get married so he has someone to help w/his daughters? Why are you getting married if you have the means to support a household on your own?  Marrying a person ideally means that you are joining as one and building a life together. It sounds like you don't want to have a life w/him but one completely separate. 

"Because I loooove him..." is so fleeting. I'm sure you felt the exact same way about your DD's father at one time as well. I stupidly married for luuuuuv and both times ended in divorce.  You only really learn what marriage is really about when you split; money, property, resources, sex and power. Elderly couples who have been together for decades were more committed to staying together than in love. If these things were picked apart and agreed on before tying the legal knot there would be less marriages and consequently less divorces.  

Please try to get to the real reason of WHY you're in a rush to marry this man and why does he want to marry you? What is the ideal you are both seeking then what is the reality?  You may want to try some premarital counseling.

Best of luck!  

I for one do not think that a split living arrangement is conducive to a successful marriage. If you and he cannot be together than he isn't the right guy and now isn't the time.

Either figure it out, hold all of the kids to a reasonable standard of behvior and parent together as equity life partners and equity parents to any children in the home regardless of kid biology ... or ... don't waste your time.

IMHO of course.  Good luck.