Experienced Landlords Help! new tenants, leases, screening

[Chris Y.]

Calling for experienced landlords. 

I bought a property with tenants (a couple with a kid) already in it.  When I bought the property, it was managed by a property management company, so the lease was with that company. After the sale, I started managing the property myself. 

I just learnt that the couple split and the lady moved out with the kid. The male tenant brought in two ''friends'' and it had been a few weeks before I knew it.  So that was against the original lease which requires landlord's consent before subleasing. 

So now I have asked the two new tenants to fill out applications and I am planning to do background/credit checks on them.  My questions are:

1. Should I sign a new lease with all three of them ?  The original lease was with the couple and now the lady moved out so it is no good anymore I suppose.   I do not know how long the two new tenants are looking to rent. 

2. What if the two 'friends' are just looking for short term rent, so should I allow the subleasing to allow the flexibility?  But I have read about many posts about the downside of subleasing? such as eviction, trashing, responsibility etc.....

3. I do not have a standard lease for them to sign, can I just use the original lease from the Property management company, just removing the company's name ....

Thanks very much