I am making an open-sourced font that is based on IPA Font License Agreement, and I would like to include some glyphs from a SIL Open Font License font. Are these 2 licenses compatible and how should I release the font? Would I be forced to use one of the License only or can I license the font with two license in one font file?
Are these 2 licenses compatible and how should I release the font?
No, the IPA Font License Agreement and the SIL Open Font License are not compatible with each other.
Both licenses require that once a font is released under that license, then all modifications must also be released under that license. The OFL even explicitly states that a derived work must be entirely under the OFL license and no other license.
If you create a new font that is in part based on an IPA font and in part on an OFL font, then the only way to obey the restrictions that both licenses put on you is to keep the new font entirely private (no distribution at all).