Everyone jumping the gun without reading carefully. There is a part not shown in the exchange between Nino and Yotsuba. It feels like Yotsuba went to Nino first and told her that she rejected him so Nino can have her way instead. Nino definitely won't accept that, so she uses an ultimatum to force Yotsuba to prioritise herself.
Same with Miku. It's her way of forcing Yotsuba to think of herself. Both are definitely dealing with being rejected too, so jealousy might be mixed into their method. That doesn't mean they have completely lost it.