Hi! For sure TV shows and sitcoms can help in the learning process. Be aware that usually they are played on American slang and this could be a bit difficult to understand, especially in the beginning. In particular "Modern Family" has a rapid pace and an intense language. It could be markedly challenging and I think it's really useful especially at an upper-intermediate level. For a beginner I would recommend a slower and easier pace.

Is it suitable for learning English? Absolutely, depending on your proficiency level. It's a popular show because it's funny, so it's a great way to stay motivated while you learn English. A lot of the humor is situational, meaning you laugh at the situation, not necessarily at what they say. However, if you don't understand 95-98% of the spoken content, you will need to spend a lot of time studying to understand the episodes. If you are at an intermediate or high intermediate level, watching the show can be effective, but you'll have to dedicate time to studying. Advanced learners can learn a lot of vocabulary through context, without dedicated study time. I hope this answered your question!

Yes it is. In my opinion very good source.