To answer, "Is it allowed to offer Jummah prayer inside the house when moving outside could be dangerous and/or life threatening?". I would say yes, praying from house is allowed in case of real severe hindrance. I base this off the hadith present in both Bukhari (668) and Muslim (699). I will quote the one in Muslim, because I feel like that one is easier to read. Though, I have linked both.
When you have announced" I testify that there is no god but Allah; I testify that Muhammad is the Messenger of Allah," do not say:" Come to the prayer," but make this announcement:" Say prayer in your houses." He (the narrator) said that the people disapproved of it. Ibn 'Abbas said: Are you astonished at it? He (the Holy Prophet), who is better than I, did it. Jumu'a prayer is no doubt obligatory, but I do not like that I should (force you) to come out and walk in mud and slippery ground.
وَحَدَّثَنِي عَلِيُّ بْنُ حُجْرٍ السَّعْدِيُّ، حَدَّثَنَا إِسْمَاعِيلُ، عَنْ عَبْدِ الْحَمِيدِ، صَاحِبِ الزِّيَادِيِّ عَنْ عَبْدِ اللَّهِ بْنِ الْحَارِثِ، عَنْ عَبْدِ اللَّهِ بْنِ عَبَّاسٍ، أَنَّهُ قَالَ لِمُؤَذِّنِهِ فِي يَوْمٍ مَطِيرٍ إِذَا قُلْتَ أَشْهَدُ أَنْ لاَ إِلَهَ إِلاَّ اللَّهُ أَشْهَدُ أَنَّ مُحَمَّدًا رَسُولُ اللَّهِ فَلاَ تَقُلْ حَىَّ عَلَى الصَّلاَةِ قُلْ صَلُّوا فِي بُيُوتِكُمْ - قَالَ - فَكَأَنَّ النَّاسَ اسْتَنْكَرُوا ذَاكَ فَقَالَ أَتَعْجَبُونَ مِنْ ذَا قَدْ فَعَلَ ذَا مَنْ هُوَ خَيْرٌ مِنِّي إِنَّ الْجُمُعَةَ عَزْمَةٌ وَإِنِّي كَرِهْتُ أَنْ أُحْرِجَكُمْ فَتَمْشُوا فِي الطِّينِ وَالدَّحْضِ .
Sahi Muslim Book 6, Hadith 35
Note that I said, praying from home is allowed, and did not necessarily call it the Jumu'a prayer. I refrained from making a more definitive statement because I quoted the hadith and you can read it and think more for yourself. I have often been told that upon missing Jumu'a you pray Dhuhar instead because if you missed the two fardh of Jumu'a then you have likely missed the jamma`t or the khutbah and the point of the Jumu'a prayer is more so to gather, listen to the imam and then say the two fardh. Therefore, if one has missed the point of attending the jamma`t as well as the khutbah and then misses the two fardh on Friday, it makes sense to instead pray Dhuhar. This is just a chain of thought and I understand that this does not mandate much but you can do further research to extend your own understanding.
Further you ask, "How do we know our jummah or any other prayer is being accepted?", We can not. Allah is generous but this is not a science where you will have evidence, or receipts of a prayer being accepted. We should make our best efforts and hope for Allah's mercy.
"How do I make up for the Jummah prayers I have missed for months?", I am not an Imam so I don't have an acute answer for you. But, If I were to say then start praying Jumu'a and other obligatory prayers, give zakat and follow all the five pillars of Islam. Try and be a muslim to Allah; I recollect an advice which might be a hadith but I am not sure (so if someone can find it, do edit my answer). It was that if you want to know about that status of your repentance than it has been accepted if you have managed to refrain from whatever wrongdoing that you were previously involved in. I find this to be reforming because it causes one to rethink twice before traversing the same mistakes because if you have refrained from them thus far, as far as you know, you were forgiven.
And when those come to you who believe in Our verses, say, "Peace be upon you. Your Lord has decreed upon Himself mercy: that any of you who does wrong out of ignorance and then repents after that and corrects himself - indeed, He is Forgiving and Merciful. Quran 6:54
Hope I at least helped some.