Multiple transactions to one address I am having some trouble understanding the following. Lets say Alice, Bob and Charlie all sends me 1 BTC each to the same address. I want to transfer 1.5 BTC to Dennis, would it then take Alice and Bob's UTXO and send it, or would it take Alice, Bob and Charlie's unspent transactions send it and then resend me the 1.5 BTC as change?

I understand that is how it works with wallets, but I am unsure if an address aggregates UTXO, or whether they still remain separated.
You would only need to use Alice and Bob's UTXOs to transfer 1.5 to Dennis. You would then get a new UTXO worth 0.5 sent to you as change (minus network fees). This would leave you with your origional UTXO worth 1 BTC from Charlie and a new UTXO worth 0.5 BTC from your transaction to Dennis.