The literary works and their authors are matched up incorrectly in two of the pairs and correctly in the other two.

1. Devichandragupta: Bilhana - This is incorrectly matched. Bilhana was not the author of Devichandragupta. However, Bilhana famously wrote the Vikramankadevacharita, an epic poem describing the victories of the Chalukya king Vikramaditya VI. The author of Devichandragupta is Vishakhadatta.

2. Hammira-Mahakavya: Nayachandra Suri - This is correctly matched. Nayachandra Suri was a renowned Jain monk and author of Hammira-Mahakavya. This work is a famed historical poem about the life of Hammira, a Chauhan king of Ranastambhapura in Rajasthan.

3. Milinda-panha: Nagaijuna - This is incorrect. Milinda-panha, also known as Questions of Milinda, is an ancient Buddhist text that presents Buddhist doctrine as a dialogue between a Buddhist sage named Nagasena and the Indo-Greek king Menander (Milinda). The author is not known, but certainly, it's not Nagarjuna. Nagarjuna is the philosopher who founded the Madhyamaka (Middle Path) school of Mahāyāna Buddhism.

4. Nitivakyamrita: Somadeva Suri - This is rightly matched. Nitivakyamrita, a work on political ethics, was written by the famous Jain Ascetic, Somadeva Suri.

Therefore, if we go by the given options, it is clear that "Only two" literary works and authors have been correctly matched - Hammira-Mahakavya: Nayachandra Suri and Nitivakyamrita: Somadeva Suri. So, the correct answer is "Only two".