Only child, resentful of my adopted siblings . . .

I come from a family, 2x adopted 2x bio of which the 2 youngest are adopted.Yes I feel I can't express how I feel if it's at all negative, I feel guilty and unkind, and very much in the wrong for even thinking that there would be a difference between myself and my brothers and sisters. I can totally relate to your drowning kittens analogy. I'm never 100% sure whether my unrest is because of normal sibling feelings or because of adoption.I felt completely pushed to one side when my brother was adopted (3yrs younger) but accepted the arrival of my adopted sister (6yrs younger) Our father died prematurely. My mum formed a very tight bond with my adopted sister, she had treated her in a much more preferable way than me and my adopted brother who has always received more emotional attention because he 'needed' it because he was adopted.I just feel I have slipped through somehow, because I've not 'needed' attention.Both my sister and myself are single parents having had failed relationships both having two boys. My sister (never left home her partner originally moved in) lives with my mum with her children. Where as I have always been made to be independent.As our children have got older it has been progressively difficult for me and my children to visit as there 'is not enough room' where as my sister does not cook, pays an unrealistic contribution to housekeeping, my mother has been with her throughout both her labour's, chosen her children's schools, looks after her children to enable her to work, takes her on holiday three times a year (of which we are invited to come with them both for one, i am not ungrateful, but always feel a bit of a spare part) when I speak to my mother on the phone I hear her in the background quite often pottering nearby, our calls have been interrupted many times over the years by my sisters kids.My sister and her children have better material and emotional support, I always used to think 'oh well, lucky them that they have eachother'. In all honesty this explain is just the half of it. In contrast I was told to stand on my own two feet, man up, take responsibility, if its hard get harder, all of this and my life has been so hard I eventually crashed with exhaustion, twice.I just think mum has over compensated at my expense. My kids are now in their 20's mum has had a good job so has often given us handouts, but it's got to the point where we are saying no thank you because the relationship just isn't there, and it's feels like payment in exchange.Regretfully unlike you, who has so considerately chosen to not say anything to your parents, I have, firstly my son did. This is so sad as I shouldn't have because I don't think this can now be repaired.Unfortunately although over the years I have tried to be objective about adoption being the issue, I think it is. Mum overcompensates and has made considerably more effort to bond with my younger siblings, sadly for me, my older brother had the bonding that a first child has and when our dad died it was him mum wanted for comfort although I tried.This makes me pretty miserable. And very lonely. I really feel rejected and not needed as mum has my sisters family at home.Believe me I do want to see children looked after as part of a family and know adoption to be correct, but parents need to be fair, and loving all round. They should be very aware of over compensating, I am sure that all the while my mum has assumed I am ok because I know I'm hers biologically. Not always so.