First Rental Property

[Nuno Pereira]

Hi everyone, my name is Nuno and I'm extremely excited join the BiggerPockets.com community. Around April 2017 i started reading a lot of real estate books and after two-three months of learning (almost 6-8 books), I decided to buy a new home in a better neighborhood and turn my old house into a rental property. 

I used the knowledge I learned to go through the process of scheduling the showings, doing the showing, taking applications, and screening tenants. After a 2-3 weeks, I finally accepted an application and sent the tenant the acceptance letter to a family of three adults and two children (husband, wife, wife's mother, and two boys). I sent a follow-up emailed to the applicants to schedule the lease review/signing and I explained that all adults have to sign the lease. They responded to me via email requesting to not have the wife's mother sign the lease agreement and that they are making other living arrangements for the mother so her stay is temporary. I was hesitant to adhere to their request because everything that I've read tells me I should have all adults sign the lease agreement. I ended up responding saying that the wife's mother has to sign the lease to acknowledge that she understands the rules listed on the lease agreement. I also mentioned that only the two heads of the house hold (husband & wife) are responsible for paying the rent. They didn't seem too happy with my response so I have been wondering:

1. Am I doing the right thing by insisting that the wife's mother sign the lease? 
2. If the applicants ask me to add a clause to the lease agreement to specify that the wife's mother is not responsible for the rent, should I do it?

Thanks in advance for any advice!

- Nuno