Co-tenant exiting and deposit

Apologies in advance for the long post, I've spent some time going through threads looking to see if there are any similar experiences but couldn't find anything recent. I'd be really grateful if anyone could point me in the right direction to get more info/advice on this issue.

A bit of background on the situation, there are 3 of us living in an apartment, all named on the tenancy agreement and we have 12-month fixed term contracts that have rolled over for a number of years. At present, our fixed term contract ended in Feb 2020 and we have yet to receive a new contract from our landlord (this has usually been sent to us in April each year and we assume the delay is due to COVID). We have continually paid our rent on time and in full and the landlord has recently conducted minor repairs in the accomodation.

One of our co-tenants advised us that she would be moving out from the accomodation and would be looking for a new tenant to replace her on the lease. This has occurred in the apartment before without any pushback from the landlord. The tenant originally planned to sublet the room for 3 months and advised us of this apx 2 weeks ago. On Friday, the tenant advised us that the room was now available permanently to a new tenant and updated her advertisements accordingly. Our June rent payment was due today and the ex-tenant failed to pay her rent and advised us that she is planning to get a new tenant to backpay her part of the rent (we believe this is unlikely to happen). The remaining two tenants paid the rent in full to ensure on time payment to the landlord.

Conscious of the restrictions imposed on tenants regarding moving new people in due to COVID, are we as co-tenants permitted to withhold the ex-tenant's deposit in order to cover the missed rent payment and lack of sufficient notice to source a replacement tenant?

Thanks in advance.