Note: I am going to use 3rd person plural pronouns (e.g. "they", "their") when referring to my child as I think gender is not important here.
My wife and I are using the One-parent-one-language (English & Hungarian) approach to raising our child bilingual (since their birth) in a country where my wife's language (English) is the official language. I am the only one who speaks Hungarian in our environment (house and community), besides the occasional video-call to my parents. As our child did not start speaking until after we started wondering whether their non-speech has any other causes besides the two languages being used, to encourage their speech, I did not "demand" Hungarian to be spoken to me (essentially interpreting the child's English words as if they were spoken in Hungarian). Our child is now 2-and-a-half years old. I am spending about 30% of my child's awake time with them (more on weekends, less on weekdays).
This approach was effective enough that our child understands both languages, but when speaking, they prefer English (which is to be expected, given the above). They do use Hungarian words sporadically in their sentences (mostly ones they do not seem to know the English equivalent of, and mostly nouns).
My wife is fully supportive of our approach and goals so far, although she does not know Hungarian (due to busy schedule this isn't going to change anytime soon).
We are not planning to move any time soon, although a short (e.g. one- or two-week long) trip about once a year to Hungary (to visit my parents and other relatives) is planned.
My mother is currently scheduled to help us out for two months (my wife's usually part-time work schedule will increase during this time), arriving in a week's time.
I would like to encourage our child to start speaking (more) in Hungarian to me (and to my parents).
What I have tried:
Speaking and reading a lot of Hungarian, and playing/singing Hungarian folk and child songs to our child. I am planning to start playing some (read-aloud) children's stories in Hungarian as well to introduce a variety of voices speaking the language.
My attempts to suddenly "enforce" the use of Hungarian (wanting to hear them ask for their wants in Hungarian and/or "not understanding" non-Hungarian) was met with active resistance on my child's part to the point where they would rather chose to abandon their wants instead of speaking the words in Hungarian, even when all they would have had to do was to repeat the (Hungarian) words I intoned to them back to me. As this ended in a lot of frustration (on both ends) and in even less exposure to Hungarian, I gave up on the idea in a few day's time (further reinforced by comments to other questions on bilingual child raising on this site). (*)
(*) The above behavior on our child's part might not be (solely) related to speaking in Hungarian as they today exhibited the same behavior (refusal and giving up on the object of "want") when my wife wanted them to start saying "please" and "I would like" instead of "I want".
I tried to look for other Hungarian-speaking people in my community, but I was so far unable to find a community that would regularly organize meetings where we could go to for more exposure to Hungarian (I have heard of other Hungarians being in the area, but it appears there is no "organized" community to speak of).
Sometimes when I genuinely did not understand what our child was saying, I told them (in Hungarian) that I did not understand, and sometimes they repeated their request in Hungarian. I have not yet tried to actively "exploit" this as an attempt to get them to speak in Hungarian.
What options/methods do I have to encourage our child to start/try to actively use their knowledge of Hungarian? The result does not have to be in the short-term (although that would be preferred).
How can Grandma's upcoming visit support the above options/methods? Besides the obvious benefits (she is going to be with her grandchild almost 24/7 while visiting, so exposure to Hungarian will be increased), how can we transition these benefits to after her departure?