If the tenant is still present at settlement, you will still be eligible for your grants and stamp duty exemption as long as the tenant vacates reasonably soon and you can commence your initial 26 weeks.
It would be wise to check the tenant's lease prior to exchange of contracts to ensure you will have the right to evict them in time to commence your residency requirements.
As the eligibility criteria are constantly changing, it would be a good idea to check with the Office of State Revenue about your exact circumstances prior to exchange of contracts.