بسم الله الرحمن الرحيم
(Fatwa: 1056/1078/N=10/1437)
If complete glans get into the vagina of your wife and it was done while keeping the fast which was remembered then the fast of both of you came to an end though no discharge took place. In this case, qaza and kaffarah both became wajib on you. Only istighfar is not enough, however both of you should do istighfar with qaza and kaffarah. You should keep sixty fasts continuously as the kaffarah of Ramadan. Thus both of you would keep sixty one fasts each one for missed fast and sixty fasts for kaffarah.
وإن جامع المكلف آدمياً مشتهى فى رمضان أداء، ………أو جومع أو توارت الحشفة في أحد السبيلين أنزل أولا ، عمداً ……قضى،…….، وكفر ……. ككفارة المظاهر (الدر المختار مع رد المحتار ، كتاب الصوم ، باب ما يفسد الصوم وما لا يفسده 3: 385-390، ط: مكتبة زكريا ديوبند).
Allah knows Best!
Darul Ifta,
Darul Uloom Deoband