Is there a way to learn Srimad Ramayanam, Mahabharatam, and Bhagavad Gita as per our samparadayam through santhai form? If not, why? Are these Kalakshepa granthams?

Do not understand under what aspect you have asked to learn.
Srimad Ramayana kalakshepam has been conducted at all places, at least partially or in a summarized form.
There are 24,000 shlokas in Ramayanam and Mahabharatam consists of a lakh shlokas. Learning them all will take a lifetime; no one will teach each shloka and there is no need to do so because all these shlokas are simple. It has been in practice to listen to these shlokas through preceptors. Both Ramayana and Mahabharata are similar in terms of authenticity. But as per sampradayam, few specific portions in Mahabharata are rendered as kalakshepams, unlike Srimad Ramayanam. Initially, we can obtain it as preaching from Acharya and later learn it on our own.