Complex sentence: While Richard Whitney was and assumed to be a brilliant financier, he in fact had personally been involved with speculative investments in a variety of businesses and having sustained considerable losses, began borrowing heavily from his brother George as well as other wealthy friends.
Split into simpler sentences: While Richard Whitney was assumed to be a brilliant financier, he in fact had personally been involved with speculative investments in a variety of businesses and had sustained considerable losses. To stay afloat, he began borrowing heavily from his brother George as well as other wealthy friends.