A point that has not been made enough on this thread is that if the kids lose their minority language that will directly impact their relationship with their othergrandparents, OP's parents. Personally if my kids married someone from another culture I would take an interest in the language long before kids came along.
This is such an important point. And the reality is that maintaining a language-other-than-English in an English-speaking country is really hard, compared to doing it the other way round (we are a bilingual family in Japan and do English as well as Japanese, maintaining English as a home/minority language is pretty easy by comparison). In English-speaking countries, English tends to overwhelm the other, minority language and it's really easy for the kids to gradually stop speaking it.
This makes it harder for them to have a close relationship with other relatives overseas, and can affect the power dynamics of the household in a weird way.
In the OP's case, she is actually a native speaker of English as well, so it's a bit different. But when you have immigrant parents who are not native speakers of English, it can do odd things if the kids end up speaking only English and the parents end up speaking it to them all the time.
It's hard to discipline someone seriously or really lay down the law in your non-native language, esp if your grasp is tenuous, so it makes it harder for the immigrant parent to discipline their child appropriately or have control over the household.
The kids will rapidly acquire completely fluent, native-level language that is far better than their parents, and during the "arsehole teenager" phase may use this to their advantage - deliberately talking too fast or at too high a level for the parent to understand, talking to each other in ways the parents can't follow.
If the immigrant parent can't talk to their kids at a "high" level, this creates gaps as the kids get older; the family is less likely to have interesting or stimulating conversations around the table about books or current affairs or the wider world, and conversation is likely to be more desultory and limited in nature.
Often the kids (who are fully native speakers) may start to dominate the conversation as they get older - discussions may start to consist largely of the kids pinging the conversation back and forth among each other at fast native speed, while the parents turn this way and that, trying to understand them and not really being able to. It's not good for the dynamics of a household when the household language is the one where the kids/teens have the upper hand over the parents.
Finally, sometime dementia causes older people to lose their "non-native" language. If, as an immigrant, you don't teach your native language to your kids, you may end up literally unable to communicate with them at the end of your life.
All these are reasons why many parents are really protective about their language and teaching it to their kids. Having a more flexible language policy when kids are much older is one thing. But when kids are little, many parents prioritize making sure that their kids get a secure base in their language, and with good reason.