Question: My first year undergraduate teammate has submitted our project work to multiple conferences. I want him to pull back the submission before reviewers take action against us. But he wants proof that conferences actually care about it and can detect self plagiarism and double submission.

This is in electronics, where conference proceedings count as publications.

Answer: 
Organizers of conferences with overlapping review periods sometimes exchange the submission information to detect cases of multiple submission. However, since doing so without the authors' agreement would be a breach of confidentiality, this can only be done ethically by conferences who announce this process in their call for papers (In my field, that is the case for several top conferences, including FSE 2019 and ICSE 2020).

There are several other ways how the duplicate submission would eventually be discovered. Let's say the paper has been submitted in parallel at two conferences called A and B.

1. There could be a shared reviewer for conferences A and B who notices the duplicate submission. In this case, the reviewer would probably contact the chairs of both conferences, leading to an immediate disqualification of the paper. Note that such a reviewer would not have to be a program committee member at both conferences: program committee members often delegate their workload to colleagues in order to reduce their workload.
2. If the paper is accepted at conference A, the paper is eventually published in A's proceedings. In this case, the reviewers from conference B might become aware of the submission of the paper to A. Consequently, they could contact the chairs of conference A to enforce its retraction.
Submitting without the approval of all authors is obviously wrong. 

Putting that aside, what’s the problem with submitting to multiple conferences? Its not the same a dual publication of journal articles - a permanent citeable record. 

I routinely submit work to two conferences - it’s in the remit of both, but there is virtually no overlap in attendance. Presenting work at multiple conferences improves visibility and networking.