In short, the answer is yes, with the right skills a hacker could get into most networks as has been seen with highly sophisticated attacks on large networks. The question though would be why?
To access devices on your network would take time and effort, most large scale "hacks" are done by bots which simply send a link of some kind, you open it and then you've given the bot access to your data.
The safest way to protect your network would be to change any of the default passwords to secure passwords and this will fend off most attacks. For example, in theory if a hacker was to access one of your devices connected to your router, they could potentially access the admin area of the router remotely and see what other devices are connected. This is still a long way off actually accessing those devices though.
