No they should not be excluded
Being biracial and feeling completely excluded by both parts of my heritage growing up, this question solidifies exactly why biracial people feel anger towards being born into two races. Never belonging or fitting in anywhere. Even having a group which is only made up of biracial people is exclusionary in itself. It’s purposefully othering. Biracial people should be able to join either group knowing they won’t be ridiculed for being ‘too white’ ‘too Chinese’ ‘too black’ etc. Why should we have to shut the door on one part of our genetics to appease people who are clearly lacking the intelligence to comprehend we don’t just fit into just one box?
Where do any biracial children or parents fit in anywhere then? Where do you think they are allowed to ask about their (half/portion) of their background for advice other than their own family which may be the issue to begin with hence wanting to ask for outside advice? You can make up an infinite amount of groups for their specific genetic make up. Is there a 1/4 polish 3/4 Ukrainian group in here? YES someone is allowed to ask and give advice for a group to which they are associated. You are not allowed to judge someone for how much they relate to (or "look like") each/any part of their background.