What flexes?
There must be a point of flexibility in every project; either Scope, or Date.
If the due-date won’t flex, scope must flex. If the scope won’t flex, the due-date must flex.
Even Apple’s iPhone famous launch keynote had a flex point (scope). They had several phones lined up behind a table, each only capable of doing one thing.
If there are no points of flexibility, your team will burn out and leave you, as they should, because they’re being tasked with unhealthy and unsafe scopes where the only possible casualty is them.
Scope, or Date. Make sure everyone knows which one it is, make peace with it, then do your very best.