Rented to early lost out on hundreds monthly, raise rent?

[Sherwin Vargas]

Own a single family, after looking at comparable rentals and talking to agents that work in the city we decided to rent at $1750 a month.  A month later 2 bedrooms went from 650-750 a month to 1100 a month( my house is a 7 bed 3 bath with garage and yard space. not having much experience was probably the cause and listening to friends and family/the rental agent since i wanted to charge 2000 a month. tenants lease is almost up, great family really trying to get their finances together to buy the house within the foreseeable future. 

Should I raise their rent to market prices? probably 2200-2500 a month or leave the same since they want to buy the property within a year or two and really take good care of the property? 
Should I also draft up a contract with a nonrefundable deposit giving them a time frame to purchase the property? we are ready to sell since their lease is up but are willing to wait for them to be ready to purchase

Just looking for your opinions and thoughts