issue with tenant not following 60 day notice

Hello all,

Looking for constructive feedback with this post.

I have tenants who have been there almost 1 year- they have been good overall- paying on time and keeping the home in good condition. I did the walk through more than 2 months prior to lease renewal and they said they wanted to stay at the walk through. I emailed them a copy for the new lease to be signed approx 2 weeks ago. The lease ends June 30th. They called me on June 23rd and said they got a great opportunity they couldn't refuse- for a property same rent as they are paying with me, and has pool and is on the water. They said they didn't want to renew the lease but wanted to stay an extra month- till the end of July and asked to apply the last months rent (given in advance) for July. I said I would get back to them because this was pretty unexpected. 

I have a company that prepares my leases and I contacted an attorney at this company. He said that because they did not provide 60 days notice the penalty according to the lease is 1 months rent.

I emailed the tenants letting them know that  1 month's rent was the penalty for not providing 50 days notice, but I also let them know that I would give them 2 options

1. they could move out July 15th- I would apply last month rent for July and they I could find a tenant sooner/get the unit ready.

2. they could move out July 31st- I would apply last month's rent for July and they would owe a half months rent penalty for not giving 60 days notice.

They emailed me back saying they were being punished and they were "disappointed".

I am managing several rentals completely by myself. I have other responsibilities in home and other work that I also manage alone- and the last minute notice from them will affect me financially- especially in the current market.

I was wondering if anyone would do something differently in this situation? Thanks