Ukraine never had nuclear weapons. Russia is the sole legal successor of the USSR and these were all Russian nukes on Ukrainian territory.
> in exchange for peace from Russia
There isn't a single mention of nuclear weapons in the Budapest Memorandum.
Structuring the breakup so that the nukes are Russia's is not really different than Ukraine giving up the nukes on its territory.
Where did they draw the line? Obviously not all USSR assets are now Russian assets, as Ukraine still has (or had) its own stockpile of Soviet era weapons, and other things like Soviet era airfields.
What split of Soviet debt obligations? Russia took over all Soviet foreign debt, as well as all the foreign assets
https://web.archive.org/web/20170312052208/http://www.cfr.or...
Points 4 and 5 mention and are about use of nuclear weapons.
I think the memorandum was intended to be a security guarantee to Ukraine after they (and Belarus, and Kazakhstan) joined the NPT and transferred formerly-Soviet nuclear weapons to the Russian Federation. I don't know why anyone would suggest otherwise.