I have two tenants for a condo.each paid half deposit/1st month etc..1 tenant personal situation has changed and he is considering leaving mid-lease.the remaining tenant has a partner who is willing to move in as a replacement so to speak. does this constitute a break of the original lease and a new 12 month with the partner re-instated?

Deduct from HER Security Deposit for pro-rated days either of them are there, and demand payment from her if SD doesn't cover it.

I'm not sure how long the renters will stay, but we have security deposits to try to keep things long-term. 

You will receive the security deposit in Checking but then transfer it to Savings.

There are costs associated with purchasing properties such as earnest money deposits, option fees (if applicable), closing costs, deposits for contractors and utilities, etc. 

Think of all the things that could go wrong and see if the lease addresses them: unauthorized pets or tenants, early termination, security deposit, lease violations, late rent, eviction, lawn maintenance, parking, etc.5.

The seller is aware of the eviction situation with this tenant.The company handling the closing asked for the security deposit amounts and I am unsure if I can put down $0 for this tenant.

There's no security deposits and payments are made weekly.

I then do the REAL negotiating and get the seller to commit to a contract and give them a deposit. 

The proper way would be to establish 401k plan first, fund it, then look for a property, sign the contract in the name of the 401k, pay earnest money deposit from the 401k account, arrange financing if needed and close on the property taking the title in the name of the 401k.