What do i do if tenant won't leave at end of lease?

Speak to a lawyer.

But seriously, if they've been there more than 6 months, the lease is pretty much irrelevant.

Lease means nothing once they are there over 6 months. They have rights now and if you want them to leave then you will have to give them the proper notice, in the proper way and for proper reasons, by law.

Is there any reason you wouldn't let them stay on?

Or without consulting a lawyer before renting out their multi-hundred thousand euro asset.

You need to get over the idea that residential property letting is just a matter of an agreement between 2 adults where both parties can set out the basis of the contract and what their expectations and obligations are. Maybe in the good old days, thats the way it worked, but not any more. There is a raft of legislation which over-rides any agreement you might have, or any lease that you have both signed.

You cannot just walk in and change the locks because there is a lease with an end date. Any mistakes you make will cost you a large amount of money when your tenant brings you to the RTB. A number of posts have suggested involving a solicitor - that is the only way forward if you dont want to make an expensive mistake.

You may not agree with the system we have, but you have to play the game by the rules, even if the rules are unfair and bizarre.

Is there any other area of law where the power imbalance between the parties to the contract is so large? Nope.

Employer /employee?

OP, you need to be careful how you handle this.

Why do you want them to move out OP?

Or maybe not familiar with the law regarding tenancies. I know of a 3 agencies who only rent to non-EU, in the hopes that if a dispute arises, they'll have left country and won't pursue it.

The positives:

Your tenants have paid rent/billsto date with no arrears. (Im presuming).

The lease should stipulate your entitlement to inspect the property with due notice, at an agreeable time … hopefully it’s in good order. (You would have an idea of this already I presume?) This would give an opportunity to speak with them.

Perhaps you’d be willing to renew the lease?

I’d focus on communication, surely you have contact details for the other tenants? You won’t have a clear idea of the situation until you talk to them.

No, you can't end their tenancy simply because their fixed term lease ends. As they have been in the property for more than six months, they now have a Part 4 tenancy of unlimited duration, and their tenancy can only be ended for certain allowable reasons. Citizens Information has a good overview of the various permissible reasons to end a tenancy. If none of the listed reasons apply, then you can't terminate the tenancy.

If one of the listed reasons does apply, you must issue a valid notice of termination in writing (not via email or text) and also submit a copy to the RTB. The notice must follow a very specific format and include specific supporting documentation depending on the reason. You would be well advised to use the appropriate sample notice of termination from the RTB as a template, as getting anything wrong in the notice will usually render it invalid and will mean you'll have to issue a brand new notice, which resets the clock on the notice period.

Keep in mind you must abide by the notice periods as well. If you serve notice before their first year is up, the notice period would be 152 days at this stage, so you won't be getting them out before September regardless. If you don't issue the notice until after they've been there a year, it's 180 days. You can issue a notice of termination while the fixed term lease is still ongoing as long as the effective date of the termination is after the end of that fixed term.

If the tenant does overhold even after being served valid notice, you can't simply "walk into the property and demand they leave"; that would be an illegal eviction and will result in hefty monetary penalties for you in the end. You must go through the full process, which will involve first going to the RTB to get a determination order and then going through the courts to get an order of enforcement. Each will have multiple stages, will likely take many months each, and will likely result in the tenant being given some additional time to voluntarily vacate, so in the end the process could potentially take a couple years or more. Be prepared for a long and expensive fight, and when the tenant eventually stops paying rent (as usually happens once things become acrimonious), chances are you'll never see that money from them.

So long as the tenant receives a valid notice of termination before the six months expires, no.

It seems to me that the rights are disproportionately skewed towards tenants.

Landlord:
A neighbour of mine (retired) is unable to evict a tenant who is claiming ownership on his rental property. He was very reasonable over covid, and hasn’t increased the rent in years (far below the market rate). When he attempted to increase the rent the tenant wasn’t having it and will not allow him to enter the property or carry out maintenance to the outside. He’s at his wits end.

Tenant:

A friend of mine moved from a top spec apartment with her sister. Gave notice but informed letting company that she’d rather leave in 3 weeks Left it in pristine condition. The letting agency company (who own the complex) commented how clean it was. However charged extra for ‘time to get new tenants’ without the month notice. Few minor marks on wall behind hobs -wiping the paint wore paint off (incorrect spec paint for kitchen). Agent said the whole kitchen would need a repaint. Long story short, they moved out …new tenants moved in 3 days later. Agent kept €600 deposit. Plus inconvenience costs for 3 €1800 , plus (there were three living there) Robbery.

I'm not sure that your second story supports your claim that "rights are disproportionately skewed towards tenants".

As to the first story, you don't say why the landlord has been unable to evict the tenant. Has a court refused to grant an eviction order? But you do say that the tenant is claiming ownership of the property. There are not many countries in the world where the courts will evict an occupier of property while the ownership of the property is in dispute; you have to resolve the ownership question first and then the eviction order follows or doesn't follow, depending on how the ownership dispute has been resolved.

Yes we do need to do more to make the rental market better but having amateurs landlord's who have no clue about legislation is not the way forward.