All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
First of all, may Allah reward you for your kindness to your mother and your keenness to take care of her matter. As long as she needs your closeness and help, as you mentioned, then in this case you are excused for not attending the Friday and congregational prayers as stated by the scholars, such as Al-Kharshi in his explanation of Mukhtasar Khalil. He mentioned the excuses that make it permissible to fail to attend the Friday prayer and the congregational prayer [among which is]: “Whoever has a sick person to take care of, especially if the sick person is a mother or a father.” [End of quote]
As for the Hadith that was reported by Abu Dawood, Tirmidhi, an-Nasa’i, Ibn Majah and Ahmad that the Messenger of Allah said: “He who leaves the Friday prayer for three consecutive Fridays on account of slackness, Allah will seal his heart.” The Prophet stated in it, as you have seen, that the one whose heart is sealed is the one who left Friday prayer negligently. The Hadiths that did not restrict that to negligence are interpreted in this way [to mean the same thing], as Al-Shawkani mentioned in Nayl Al-Awtar, when he said: “(The sealing of the heart that is mentioned is only on the heart of the one who left these prayers by negligence, so the absolute Hadiths should be interpreted to mean the same as this Hadith that is restricted to negligence, and the absolute Hadiths should also be interpreted to mean the same as the restricted ones, that it applies to one who does not have excuse, as previously clarified).” [End of quote]
Allah knows best.