Tenants want out of lease for bigger house willing to pay

[Tyrone Smith]

I have tenant that has been renting for a year and convinced me to reduce my rent and signed a 2 year lease 4 months ago. They offered to by the rental just 3 months ago and used their deposit for earnest money and walked out on deal so deposit is forfeited . Reason being they have a daughter coming to stay with them now and want a bigger house , my thoughts are decided to buy another house and want out of my lease early to pursue the purchase . They have offered up a replacement tenant but of course the system declined her  now they are offering to sign an agreement to pay me 500.00 per month the remaining lease terms? I am looking for thoughts on this situation as they pay on time and more than likely next tenants won't  and  want to know thoughts on taking a note on difference my thoughts are when they buy house they won't pay note note. They are supposedly going to rent , but they have slicked me in the past. Thoughts on how I should handle