Hello kollel!

I had a question on daf 50 of Yevamos. The gemara says that if the yavam gives a get, then has biah he needs to give a get and do chalitzah.

A few questions:

Since a get is meaningless for a yevamah on a de-oraisa basis, why cant he just do yibum and stay married to the woman?

If the get prevents him rabbinically from doing yibum, what is the status of the biah and any children that might result from it? Is she consider eishes ach? Can a decree of the rabbanan generate a mamzer in that case...even though she wouldnt even have mamzerim as a "yevamah leshuk" if she was with another man??

And if I may, two other follow on questions.

3)regarding the biah after the get, since biah is one of the modes of kiddushin, if the biah isn't valid for yibum can the yavam just intend it for normal kiddushin?

4)is maamar modeled on kiddushin or on yibum itself? Practical ramifications might be whether it can be done via a shaliach (like kiddushin) or baal korcha (like yibum).

Thank you! 8884445688

Josh