The moisture which is emitted because of foreplay is called Mathi مذي and is not Najis and it does not even break Wudhu. Semen gushes out in ejaculation. If no ejaculation, then no Ghusl is obligatory. If the wife reaches climax orgasm just because of foreplay, then Ghusl will be obligatory on her.
If husband and wife have sexual intercourse, Ghusl will be obligatory on both of them even if no ejaculation or orgasm took place as far as the penetration took place.