The sources quoted in the question suggest that there are 100,000 civilians total in East Aleppo. By this is apparently meant the entire area that was held by rebels between 2013 and 2016.
By 13 December, 98% of the city had been retaken by the Assad regime. On that day the Russian Center for Syrian Reconciliation, which is on the ground in Aleppo, said that roughly 110,000 civilians were safe in regime-controlled districts. The Center itself had counted and confirmed 95,000 civilians in East Aleppo and was providing them with medical attention and care, according to Vanessa Beeley, a freelance pro-regime journalist; the remaining 15,000 was an estimate of those not yet spotted by authorities. The official count rose a few days later to 108,000.
Also on 13 December, the Syrian Observatory for Human Rights, a freelance pro-rebel journalist group run by a Britain-based blogger which is generally recognized as a reliable source, concluded that 442 civilians were killed by pro-regime forces during the retaking of Aleppo, as well as 130 civilians killed by pro-rebel forces. It has not reported any deaths in East Aleppo since then.
On 14 December, Zouhir Alshimale, a freelance pro-rebel journalist reporting from within the 2% of the city still held by rebels, estimated that 60,000 civilians remained in his area. Reports made from within the rebel-held territory have been called into question by some media. In contrast, the professional Kuwaiti journalist Elijah Magnier -- who has been covering the war for several years and has high-level connections -- estimated that only 10,000 civilians remained.
On 16 December, the Syrian Observatory for Human Rights noted that shelling had stopped over the period 15-16 December. On that day, a Turkish-Russian agreement to evacuate both citizens and rebel militants was upheld, and thousands of militants were observed leaving Aleppo with their families.
On 17 December, Arab League Envoy to Syria -- that is to say, anti-regime source -- Staffan de Mistura estimated that 40,000 civilians remained in the 2% rebel-held pockets of the city. A day later, Reuters, relying on Syrian state television, quoted an estimate of 15,000 people (presumably including militants).
As of the evening of December 18, the evacuation has been temporarily halted because rebels are shelling the evacuation buses and threatening to murder those who ride them.
With the exception of the Russian and SOHR figures, all the other numbers here are estimates.