The answers to your questions are as follows:

1. Killing no one without the religious permission is permissible, and the meaning of religious permission is the permission of God’s Caliph on earth. Yes, in case an oppressor -whether from ISIS or other than ISIS- enters the property of a Muslim to take his life or honor, it is permissible for him (Muslim) to repel him in whatever way possible, and if he alone is not capable of repelling him, it is permissible for other Muslims to help him in this, but in case an oppressor rises up against another oppressor to overthrow his sovereignty and replaces it with his own sovereignty, it is not permissible for Muslims to help one over another, unless the oppressive ruler is Muslim and the one who has risen up against him, is non-Muslim; as one of our companions informed us, he said:

«سَمِعْتُ الْمَنْصُورَ يَقُولُ: إِذا رَأَيْتُمْ جَبّارَيْنِ يَقْتَتِلانِ بِرَمْلٍ فَذَرُوهُما يَحْثُو أَحَدُهُما عَلَى الْآخَرَ حَتَّى يَهْلِكَ الْأَعْجَز! قُلْتُ: أَرَأَيْتَ إِنْ كانَ أَحَدُهُما مِنَ الشِّيعَةِ والْآخَرُ مِنَ السُّنَّة؟ قالَ: ذَرُوهُما! قُلْتُ: أَرَأَيْتَ إِنْ كانَ أَحَدُهُما مُسْلِمًا والْآخَرُ يَهُودِيًّا؟ قالَ: إِذا كانَ ذَلِكَ فَأَعِينُوا الْمُسْلِمَ لِكَيْلا يَغْلِبَ عَلَيْكُمْ الْيَهُودِيُّ فَيَسُبَّ نَبِيَّكُمْ ويُحْرِقَ كِتابَكُمْ ويَهْدِمَ مَساجِدَكُمْ»; “I heard his Honor Mansoor says: whenever you see two oppressors who fight each other on sands, leave them to sprinkle soil over each other until the weaker one is destroyed! (means do not interfere;) I said: what is your opinion if one of the two be Shia and the other Sunni? He said: leave them, I said: what is your opinion if one of the two be Muslim and the other Jewish? He said: if so, then Help the Muslim so that the Jewish does not become dominant over you that insults your Prophet and burns your Book and destroys your mosques”!

2. Killing oneself along with killing enemy is an ignorant and non-Islamic deed; as one of our companions informed us, he said:

«سَأَلْتُهُ عَنِ الْمُسْلِمِ يَحْمِلُ فِي جَيْبِهِ ناسِفَةً فَيَرْمِي حَتَّى إِذا نَفِدَتْ سِهامُهُ وقَرَبَ مِنْهُ الْكافِرُ فَجَّرَها فَقَتَلَهُ وقَتَلَ نَفْسَهُ، قالَ: هَذَا مِنْ عَمَلِ الْجاهِلِيَّةِ كانَ إِذا أُحِيطَ بِأَحَدِهِمْ فِي الْحَرْبِ يُنادِي: اقْتُلُونِي وفُلانًا فَيَقْتُلُهُ ويَقْتُلُ نَفْسَهُ! فَمَكَثَ هُنَيْئَةً ثُمَّ قالَ: ما أَلْفٌ مِنَ الْكُفّارِ بِرَجُلٍ مِنَ الْمُسْلِمينَ فَلا تَفْعَلُوا»; “I asked his Excellency about a Muslim who carries a bomb in his collar, so he shoots until his bullets run out and the infidel gets close to him, then he detonates the bomb and kills him and also kills himself (along with him), he said: this is from the ignorant deeds, whenever one of them was dominated in a war, he called: kill me along with that fellow, so he killed him and himself together! At this time he waited a little and then said: One thousand of infidels do not worth one of Muslims, so do not do it”!

3. Initiating Jihad is not permissible except by the permission of God’s Caliph on earth.