No they can't. There's no legal liability that would extend from one person to the mother of their child if they aren't married. I'd guess even if they were married, the liability is a lawsuit couldn't extend to the spouse unless they were directly involved in the concert or planning aspects related to security and such. If Travis Scott was to lose the suit, the plaintiffs (and their lawyers) would only get as much as possible from Travis. Travis could have future wages garnished perhaps, but the saying you can't get blood from a stone is correct; if a person doesn't have as much money as you're asking for in a civil suit, you'd never get that much money anyway.