Is hiring a lawyer a good idea in this case? ?

A UK Court won't award you damages just an eviction order. You would need a Solicitor to find them when they leave and if they have no money it's pointless.
You will also loose the solicitors fees.

Morning fox, we cannot instruct Barristers direct, only a Solicitor can do that.
U.K.

Our crappy politicians enabled deadbeat tenants and the chances of you easily collecting rent is slim.  When they are leaving video and take pictures of everything they did. Any damage should be recorded.  If they don't have anything for you to collect you're getting exactly that amount.  Nothing.  So getting a lawyer is going to be a wasted expense unless they have some ability to pay you.  If they have decent jobs and if they have an ability to pay a lawyer is the way to go.  If not, just go to small claims to get a judgement.  Once you have it follow them legally and through social media and show up at work, at places they frequent and make them miserable until they make an arrangement to pay you.  Do the same every time they miss a payment by so much as three days.  If is probably the only way you'll get any satisfaction.  

Well...you can sue for damages.  Your problem is going to be how to actually collect once you win.   But yes, you should have a lawyer.  I mean even for the kicking them out part.

WHERE?  In general, yes, attorneys get better results than non-attorneys.

No judge is going to award "emotional damage" for tenants not leaving on time.

It's your own fault you've waited a year to deal with this through the courts.

Yes, if they owe you money, you are entitled to seek a judgement through the court system.  A lawyer can help facilitate this process.

Even in the UK, this depends on where. Scotland, Wales, England, N.I. (lets not discuss the Isle of Man and other places). In any case, I would talk to a regular barrister first.

Your English is fine. It's your American that seems odd.

Civil damages laws are not much different in U.K. than in the U.S.A. Unless you already filed a claim for damages relating to eviction, you can amend the complaint to include the damage done to the property. Your damage just does not include back rent with interests, but any damage that has occurred to the property other than just normal wear and tear. This may require you to consult a local solicitor or talk to one who has assisted you previously. 

Once you have a judgement, you can than seek a debt collector to hound them.  You can get liens on anything they own now or will acquire later and make their life a living hell. Debt collector will keep 30% of the proceeds. Judgement is usually good for 10 years and can be renewed for another 10, usually indefinitely until debts are satisfied or settlement reached.   

Finally, think about selling the property, it is too much stress. 

If you HAVE tenants, you can't afford NOT to have an attorney, PERIOD.

Note: If you ACTUALLY lived in the UK, you wouldn't apologize for your English. Your update is STRONG evidence you are are not a landlord and probably not even a tenant. Please tell mommy what you are doing with here computer.