| | Re: Elision of Schwa sound.
1. I don't agree that they sound like one consonant - for me, there are plainly two. However this doesn't affect the rest of what you say. But I don't understand what your question is?
2. The schwa is by definition a weak sound (it occurs only in unstressed syllables) and is therefore unstable - weaken the syllable any more and it disappears entirely - which is what happens here and in all the other examples you give. The exact consonants are irrelevant - see 3.
3. Metathesis is the "rearrangement" of sounds in a word and is fairly rare, I think, outside a couple of common examples which occur in certain accents only - eg " asked" /ɑ:kst/ rather than /ɑ:skt/ in some US varieties. It's completely different from elision, which is the omission of a sound or sounds, and which is what is happening in all your examples - the schwa is elided. As I said above, the exact consonants involved are irrelevant, I think. I'd group your examples a + b under group 2 (ie elision of schwa between two consonants) and c-e under group 4 (reduction of a dipthong to a monopthong). I don't think these examples form a separate group of their own.
4. Your transcription is off here. You're mixing a phonetic symbol [ɛ] with phonemic symbols - which you shouldn't really do. The standard phonemic transcription (ignoring the rhotic /r/) would be :
a) Swear /sweə/
b) Wear /weə/
c) Bear /beə/
d) Compare /kəmˈpeə/
e) Declare /dɪˈkleə/
f) Share /ʃeə/
g) Despair /dɪˈspeə/
h) Repair /rɪˈpeə/
i) Impair /ɪmˈpeə/
In other words, all these words use the dipthong /eə/. I understand the change you're talking about though - in rapid connected speech the dipthong might well be reduced towards a monopthong, so it sounds as if the schwa has been elided. But it happens with other dipthongs too. See the answers to 3.