1 “why is it that pesach never lands on Sunday twice consecutively?”
Pesach on Sunday is linked to Rosh Hashana on Tuesday.
In order for Rosh Hashan to fall on Tuesday the molad has to occur between noon on Monday and at the latest noon on Tuesday * The molad from one tishrei to the next is never that close together it is either 4 days 8 hours 876 Chalaikm later in the week in a regular year and 5 days 21 hrs 589 Chalakim in a leap year.
* in most years ie regular years it has to occur in an even narrower window until 204 chalakim after 3 AM (six hours note: this is using mean solar time) as mentioned in my earlier comment in this thread
2) “Why can’t Chanukah start on Tuesday?”
for Chanuka to start on Tuesday You would need Rosh Hashana on Tuesday and the year “shalem” meaning that cheshvan and Kislev both have 30 days* In such a year 1 Kislev would be Shabbos 22 Kislev would be 3 week late on Shabbos, 23 sunday, 24 Monday 25 Tuesday.
However such a year is impossible a shalem year has 355 days if regular and 385 days for leap year
For a regular year Rosh hashana would occur 355 days later ie 50 weeks and 5 days, which means Rosh Hashan would be Friday – an impossibility
For a leap year Rosh Hashana would occur 385 days later ie after exactly 55 weeks. That would mena Rosh Hashana on Wednesday – again impossible
*It doesnt matter how many days Kiselv has for this , but the choices are 29 for both chesvan and Kislev 29 for Chesvan and 30 for Kislev or 30 for both. there is no possibility of 30 for cheshvan and 29 for Kislev