I still use a video baby monitor with my 14 month old! I like to see what he gets up to when he's meant to be going to sleep! I have used 2 monitors in my house when my friend stayed with her dd. It worked fine but they were on different frequencies and different makes of monitor. It might just be a case of fiddling around with them til they both work without interference. They usually have 3 frequency settings so should be fine.