Complex sentence: There are perhaps hundreds of thousands Tirthankara idols from Surat to Decca (Bangladesh) mentioning the order, having been mostly installed by the Bhatttaraks of this order in the past 7-8 centuries.
Split into simpler sentences: There are perhaps hundreds of thousands of Tirthankara idols, spread across the country from Surat to Decca (in Bangladesh), bearing inscriptions mentioning this order. Most of these idols were installed by the Bhattarakas of this order in the past 7-8 centuries.