If Johanna's issue with Rhaenyra was that she was dancing with girls, then it's possible that romancing Alicent will sour things unless we get out ahead of it and she gets over herself. But it's also possible she's never get over herself & it's a waste of a conversation. Seems like a coin flip, either way. I read Jeyne's advice as "she's always going to hate you, so don't bother" more than "fix this now," but maybe Jeyne is wrong. We're not going to get resolution on her as a potential threat until after she has (or looks like she won't have) a son. OTOH, if relations between us sour before she has kids, she might not let us bond with our siblings.
On three way Dance - that does sound not great, but it's not like we're locked against the Velayrons right now. I'm against it, but marrying Laenor still seems like a popular idea. And if we don't we could betroth our kids and Laenor's kids or something. Or Alicent and Laenor as a lavender marriage (I'm not in favor of this either, tbh). Or one of the Velayrons or Johanna's kids could fail to have enough large dragon to be a credible faction and have to take the L and fold themselves into a faction that has a chance. If Johanna has kids when she does in canon, they'd be a non-factor.