You need to log this, either via conversation and follow up email with Management / HR, to flag the potential bullying, plus comments made directly to you about not being a part of the team. The comments about not being part of the team is actually discriminatory, however much it is a badly thought through comment made due to frustration.
Unfortunately, the employer could decide their easiest option is that you are not performing and you are not capable of doing the job, even though they are at fault for not ensuring the work load is covered by implementing a job share. How they will do this is by putting you on a performance plan to flag capability, or initiate some kind of redundancy. Therefore, like others have said, you need to be the one that raises this, logs everything, and if it continues raise a formal grievance. Also, please read up about Subject Access Requests; if they are saying these things, I can guarantee they will have emails and Teams conversations discussing it also, and if it comes to it, that is your written evidence and proof. A Subject Access Request is also a pain for any company, but it is a legal requirement for them to comply. Any keywords that identifies you (such as foster care) can be included.
Do not just hand your notice in and walk away when they are the ones who have not managed this situation.
We all understand the frustrations for your colleagues, however what you are experiencing is bullying and discrimination.
It amazes me when people write things such as "mop up work" of those on long-term sick. It is frustrating, but heaven forbid people are actually ill. The individuals gossiping and bitching are the ones who land companies in very hot water.