Only Bramhins
Pujabhi Saraswat bramhins of Lakhanpal caste have kaushal gotra.
Kayasthas have a dual Brahmin/ Kshatriya status. Source: http://samajpath.org/kayasthhist.html
Khandelwal is actually those who are having origin of Khandela location of Rajasthan. they can be Jain, Baniya and also Bramhins.
Mandrekars are from Mandrem village in north GOA and are essentially Hindu, Gawd Saraswat Bramhins (GSB)
One who has truly realised God. One who follows the Sanathana Dharma. A "Brahmin" need not necessarily be a person born in the Brahmin Varna. Even if a so called "Shudra" sincerely follows the tenets of Dharma, thinks, speaks and acts with goodness, even he/she is a Brahmin. A person for whom real happiness comes solely from being in union with God is the real "Brahmin"
The caste system at anytime is bad, it is judgemental and without love. It also became inevitable and hereditary in the later periods of ancient age due to the dictatorship of the priestly Bramhins. It also led to a power struggle between Brahmins and Kshatriyas. So they all enlarge their support to new religions like Buddhism and Jainism.