I think the decline in population in Ukraine is pretty natural, given the poverty in the country and the lack of real opportunities for many people here. It's understandable that many Ukrainians seek work opportunities overseas, mainly in other European countries. There are over a million Ukrainians working in Poland alone.
Reggie you are right about the increase in deaths in Ukraine after the fall of the USSR. But your assertion that Ukraine has too many people for the amount of land in Ukraine is not really true. Ukraine is 126th in the world when it comes to population density. Never mind the third world, but even advanced Western Countries like the UK, the Netherlands, Belgium, Germany, Italy, Switzerland, Austria, Spain and France have much higher population densities than Ukraine. So I wouldn't site this as a major issue in Ukraine.
I also agree with you that immigration won't solve the problem here. There is a strong sense of nationalism here and I am sure they would not want loads of foreigners here, even if they were to benefit Ukraine.
I have to say that it is sensible that young women in Ukraine are only having a small amount of children. It's sensible in the sense that they can't really afford many children. It is better to bring up a few children and at least give them a decent upbringing, than having many children who you can't take care of properly. Obviously this results in a decreasing population and yes it's not ideal for Ukraine as a country. But as we all know, Ukraine is a real mess and life for most locals here is really tough.