"Grandma came to our house this weekend."
I'm confused. I understood that 的 can be omitted when referring to family members or close people, but house...?
Someone correct me if I'm wrong, but I think this situation is one of many that are a personal preference, or differ based on the area of China you're hearing the phrase in. 我们家 and 我们的家 have the same meaning.
In most possessive statements, the 的 is optional, and the usage depends on what "sounds good, "e.g. 我车子 - 把那东西放在我的车里 (would sound odd without the 的) whereas 那玩儿就是我车子 is somewhat of a slang phrase where the 的 would be too formal.
But this is solely based on my experience mimicking native speakers, not in a true textbook sense of what is correct...
You can omit it before 家. Also, more generally speaking 我们的，你们的，他/她们的 is too long, and 的 tends to be omitted after these pronouns
Shouldn't the "了" be optional, since "这个周末" indicates the action was in the past?
这个周末 does not indicate past nor future. That phrase alone could refer to the weekend that has just ended, to now, or to the upcoming one.