Ukraine was home to many nuclear and rocket scientists so presumably they could have reverse engineered them if they wanted and got a big head start in it.

But yeah thats only if they wanted to try and spend the money to support a nuclear program. As they sat they were unreliable at best case.

That's false. Please stop spreading Russian propaganda. Not only Ukraine was able to control and maintaining them, in fact, Ukrainian companies manufactured nuke ICBMs, and then serviced them in Russia long after the collapse of the USSR. See, for example, https://en.wikipedia.org/wiki/KB_Pivdenne