Hi @Kilby Browne, as mentioned above, you only have a few options. You could make the sale contingent upon the property being delivered vacant at closing, but it sounds like the Seller does not want to do that.
The other option would be to have the Seller agree to send the tenants Notice to Vacate while you are Under Contract, but not having the contract contingent upon being delivered vacant at closing. This obviously leaves the risk with you that you may have to close if they do not vacate in time, but it's a hybrid solution that could work.
The last option would be closing with the tenants in place, serving them an option to renew / notice of rent increase at the market rent you want, then proceeding from there. Either they accept the rent increase or you can move forward with eviction / non-renewal procedures per the local municipality.
Things always feel a bit overwhelming when dealing with these sorts of tenant-in-place issues, but they are a lot more common than you think. I would advise finding a great Landlord-Tenant lawyer in your locale who you can run these issues by to set your mind at ease.