Family is family, and business is business. Mixing the two is more than risky.
You want to have a spouse with a Russian passport to "marry into Russia", in order to buy land?
That seems like a very 'brave' idea, considering that you have 4 kids, and as David has rightly pointed out: they should be your priority.
One thing that puzzles me is what your overall aim is - what do you need to buy land in Russia for? And why do you need a spouse for that?
There are other, certainly more serious and more respectable, ways to get into a business partnership through marriage.