Nanny with children coming over?

I placed an ad for a nanny and I got a couple responses from mothers who would want to bring their child to watch my 3 month old. One moms daughter is 6 months, another moms daughter is 2 months and another has a 1 yr old. My apartment is not baby proof and my fiancee is very weary about having other children here. He is afraid of the other child getting hurt in our apartment. We are not experienced with kids and toddlers and dont know what to expect. Is it a good idea to have other kids over when the nanny is watching her? Anyone experienced this?